configure: rework libXinerama detection a bit, remove hardcoded -lXinerama's

Make -lXinerama a dep on libDtXinerama so it doen't need to be
specified in Makefile.am files or in LIBS as it was being done
previously.

This still needs a little work, ideally Xinerama should be completely
optional and only enabled if present.  But we can save that for
later.

cde/configure.ac

@@ -265,8 +265,10 @@ AC_CHECK_HEADERS([locale.h])
 dnl libraries
 AC_CHECK_LIB(m, cosf)
 AC_CHECK_LIB(crypt, crypt)
-AC_CHECK_LIB(Xinerama, XineramaQueryScreens, ,
-                       [AC_MSG_ERROR([libXinerama not found])])
+dnl this should be configurable, for now it is required
+AC_CHECK_LIB(Xinerama, XineramaQueryScreens,
+                [SOURCE_CPP_DEFINES="${SOURCE_CPP_DEFINES} -DUSE_XINERAMA"],
+                [AC_MSG_ERROR([libXinerama not found])])
 
 dnl Special check for tirpc...
 AC_CHECK_LIB(tirpc, svc_register,
@@ -285,10 +287,6 @@ AC_CHECK_LIB(SM, SmcOpenConnection, [XTOOLLIB="-lSM ${XTOOLLIB}"])
 AC_CHECK_LIB(Xm, XmTextSetString, [XTOOLLIB="-lXm ${XTOOLLIB}"])
 AC_SUBST([XTOOLLIB])
 
-dnl Add -DUSE_XINERAMA to SOURCE_CPP_DEFINES for now.  Eventually this
-dnl should be configurable.
-SOURCE_CPP_DEFINES="${SOURCE_CPP_DEFINES} -DUSE_XINERAMA"
-
 dnl set CPPFLAGS, CFLAGS, and CXXFLAGS.
 dnl The Autoconf manual says that these are user variables and
 dnl shouldn't be modified.  It suggests that you create a special

cde/programs/dtmail/dtmailpr/Makefile.am

@@ -5,8 +5,7 @@ bin_PROGRAMS = dtmailpr
 dtmailpr_CXXFLAGS = -I../include -I../../dtcompat -I../../../. \
 		    -I$(srcdir)/lib
 
-dtmailpr_LDADD = ../libDtMail/libDtMail.a @DTCLIENTLIBS@ \
-		 -lXm @LIBXIN@ -lXinerama $(XTOOLLIB) ${X_LIBS} $(TIRPCLIB)
+dtmailpr_LDADD = ../libDtMail/libDtMail.a $(DTCLIENTLIBS) $(XTOOLLIB)
 
 if FREEBSD
 dtmailpr_LDADD += -liconv