Cleaner way to add gcc options

We can actually test for the options being accepted, rather than try
to test for gcc; this handles differences between gcc versions as well
as compilers with a similar command line set.

aclocal.m4

@@ -0,0 +1,15 @@
+dnl --------------------------------------------------------------------------
+dnl PA_ADD_CFLAGS()
+dnl
+dnl Attempt to add the given option to CFLAGS, if it doesn't break compilation
+dnl --------------------------------------------------------------------------
+AC_DEFUN(PA_ADD_CFLAGS,
+[AC_MSG_CHECKING([if $CC accepts $1])
+ pa_add_cflags__old_cflags="$CFLAGS"
+ CFLAGS="$CFLAGS $1"
+ AC_TRY_LINK([#include <stdio.h>],
+ [printf("Hello, World!\n");],
+ AC_MSG_RESULT([yes]),
+ AC_MSG_RESULT([no])
+ CFLAGS="$pa_add_cflags__old_cflags")])
+

configure.in

@@ -59,12 +59,11 @@ else
 fi
 AC_PROG_INSTALL
 
-if test "$GCC" = "yes"; then
-  GCCFLAGS="-W -Wall -std=c99 -pedantic"
-else
-  GCCFLAGS=
-fi
-AC_SUBST(GCCFLAGS)
+dnl If we have gcc, add appropriate options
+PA_ADD_CFLAGS([-W])
+PA_ADD_CFLAGS([-Wall])
+PA_ADD_CFLAGS([-std=c99])
+PA_ADD_CFLAGS([-pedantic])
 
 dnl Look for "nroff" or "groff"
 AC_CHECK_PROGS(NROFF, nroff, echo)