Update #pragmas to make clang be quiet about historic practice

This adds a #pragma to disable -Wdeprecated-register* on newer
versions of clang. We could remove all use of the register keyword
instead, as modern compilers ignore it. But it's not harmful, and
for the time being I prefer not to do doing any reformatting or
changing the historic character of this code base.

The #pragmas are removed from src/lib/libast/include/ast.h, because
they're better placed in src/lib/libast/features/common which
generates ast_common.h which is included by everything.

* https://clang.llvm.org/docs/DiagnosticsReference.html#wdeprecated-register

src/cmd/INIT/mamake.c

@@ -19,6 +19,7 @@
 *                                                                      *
 ***********************************************************************/
 #pragma prototyped
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 #pragma clang diagnostic ignored "-Wparentheses"
 
 /*

src/cmd/INIT/proto.c

@@ -18,6 +18,7 @@
 *                 Glenn Fowler <gsf@research.att.com>                  *
 *                                                                      *
 ***********************************************************************/
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 #pragma clang diagnostic ignored "-Wparentheses"
 #pragma clang diagnostic ignored "-Wunused-value"
 #pragma clang diagnostic ignored "-Wstring-plus-int"

src/cmd/INIT/ratz.c

@@ -4,6 +4,7 @@
  * coded for portability
  * _SEAR_* macros for win32 self extracting archives -- see sear(1).
  */
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 #pragma clang diagnostic ignored "-Wparentheses"
 
 static char id[] = "\n@(#)$Id: ratz (Jean-loup Gailly, Mark Adler, Glenn Fowler) 1.2.3 2010-10-10 $\0\n";

src/cmd/INIT/release.c

@@ -19,6 +19,7 @@
 *                                                                      *
 ***********************************************************************/
 #pragma prototyped
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 #pragma clang diagnostic ignored "-Wparentheses"
 
 /*

src/lib/libast/features/common

@@ -24,8 +24,10 @@ tst	ptr_void note{ standard C void* ok }end compile{
 }end
 
 cat{
+	#pragma clang diagnostic ignored "-Wdeprecated-register"
 	#pragma clang diagnostic ignored "-Wmacro-redefined"
 	#pragma clang diagnostic ignored "-Wparentheses"
+	#pragma clang diagnostic ignored "-Wstring-plus-int"
 	#pragma clang diagnostic ignored "-Wunused-value"
 
 	/* disable non-standard linux/gnu inlines */

src/lib/libast/features/signal.c

@@ -21,6 +21,7 @@
 *                                                                      *
 ***********************************************************************/
 #pragma prototyped
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 #pragma clang diagnostic ignored "-Wparentheses"
 /*
  * Glenn Fowler

src/lib/libast/include/ast.h

@@ -21,8 +21,6 @@
 *                                                                      *
 ***********************************************************************/
 #pragma prototyped
-#pragma clang diagnostic ignored "-Wparentheses"
-#pragma clang diagnostic ignored "-Wstring-plus-int"
 
 /*
  * Advanced Software Technology Library

src/lib/libast/port/lcgen.c

@@ -20,6 +20,7 @@
 *                   Phong Vo <kpv@research.att.com>                    *
 *                                                                      *
 ***********************************************************************/
+#pragma clang diagnostic ignored "-Wdeprecated-register"
 #pragma clang diagnostic ignored "-Wparentheses"
 /*
  * generate <lc.h> implementation tables from lc.tab