**/Mamfile: add header comment pointing to MAM docs (re: 6cc2f6a0)

The only proper documentation of the MAM language is in Glenn
Fowler's paper, which is unfortunately copyrighted so we can't
include it. But we can at least provide a link to it.

src/**/Mamfile:
- Add header comment.

src/cmd/INIT/mamake.c:
- Re-enable clang warnings on unused values (there aren't any).

src/Mamfile

@@ -1,4 +1,13 @@
 info mam static
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 note source level :MAKE: equivalent
 make install
 	make all

src/cmd/INIT/Mamfile

@@ -1,4 +1,13 @@
 info mam static 00000 1994-07-17 make (AT&T Research) 5.7 2012-06-20
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 setv INSTALLROOT ../../..
 setv PACKAGEROOT ../../../../..
 setv AR ${mam_cc_AR} ${mam_cc_AR_ARFLAGS}

src/cmd/INIT/mamake.c

@@ -19,7 +19,6 @@
 ***********************************************************************/
 #pragma prototyped
 #pragma clang diagnostic ignored "-Wparentheses"
-#pragma clang diagnostic ignored "-Wunused-value"
 
 /*
  * mamake -- MAM make

src/cmd/Mamfile

@@ -1,4 +1,13 @@
 info mam static
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 note component level :MAKE: equivalent
 make install
 	make all

src/cmd/builtin/Mamfile

@@ -1,4 +1,13 @@
 info mam static 00000 1994-07-17 make (AT&T Research) 5.7 2012-06-20
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 setv INSTALLROOT ../../..
 setv PACKAGE_ast_INCLUDE ${INSTALLROOT}/include/ast
 setv PACKAGE_ast_LIB ${INSTALLROOT}/lib

src/cmd/ksh93/Mamfile

@@ -1,4 +1,13 @@
 info mam static 00000 1994-07-17 make (AT&T Research) 5.7 2012-06-20
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 setv INSTALLROOT ../../..
 setv PACKAGE_ast_INCLUDE ${INSTALLROOT}/include/ast
 setv PACKAGE_ast_LIB ${INSTALLROOT}/lib

src/lib/Mamfile

@@ -1,4 +1,13 @@
 info mam static
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 note component level :MAKE: equivalent
 make install
 	make all

src/lib/libast/Mamfile

@@ -1,4 +1,13 @@
 info mam static 00000 1994-07-17 make (AT&T Research) 5.7 2012-06-20
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 setv INSTALLROOT ../../..
 setv PACKAGEROOT ../../../../..
 setv AR ${mam_cc_AR} ${mam_cc_AR_ARFLAGS}

src/lib/libcmd/Mamfile

@@ -1,4 +1,13 @@
 info mam static 00000 1994-07-17 make (AT&T Research) 5.7 2012-06-20
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 setv INSTALLROOT ../../..
 setv PACKAGE_ast_INCLUDE ${INSTALLROOT}/include/ast
 setv PACKAGE_ast_LIB ${INSTALLROOT}/lib

src/lib/libdll/Mamfile

@@ -1,4 +1,13 @@
 info mam static 00000 1994-07-17 make (AT&T Research) 5.7 2012-06-20
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 setv INSTALLROOT ../../..
 setv PACKAGE_ast_INCLUDE ${INSTALLROOT}/include/ast
 setv PACKAGE_ast_LIB ${INSTALLROOT}/lib

src/lib/libsum/Mamfile

@@ -1,4 +1,13 @@
 info mam static 00000 1994-07-17 make (AT&T Research) 5.7 2012-06-20
+note *
+note * This build file is in the Make Abstract Machine (MAM) language. It was
+note * first generated by nmake, but in the ksh 93u+m distribution we maintain
+note * it manually because nmake had too many problems to keep using. The
+note * Mamfiles are processed by mamake (src/cmd/INIT/mamake.c); we added
+note * support for indentation to improve readability. The language is
+note * documented in Glenn Fowler's paper "A Make Abstract Machine":
+note * http://web.archive.org/web/20041227143022/http://www2.research.att.com/~gsf/mam/mam.html
+note *
 setv INSTALLROOT ../../..
 setv PACKAGE_ast_INCLUDE ${INSTALLROOT}/include/ast
 setv PACKAGE_ast_LIB ${INSTALLROOT}/lib