dnl Check if the compiler supports useful warning options.  There's a few that
dnl we don't use, simply because they're too noisy:
dnl
dnl	-Wconversion (useful in older versions of gcc, but not in gcc 2.7.x)
dnl	-Wredundant-decls (system headers make this too noisy)
dnl	-Wtraditional (combines too many unrelated messages, only a few useful)
dnl	-Wwrite-strings (too noisy, but should review occasionally)
dnl	-pedantic
dnl
AC_DEFUN([CF_GCC_WARNINGS],
[EXTRA_CFLAGS=""
if test -n "$GCC"
then
	changequote(,)dnl
	cat > conftest.$ac_ext <<EOF
#line __oline__ "configure"
int main(int argc, char *argv[]) { return argv[argc-1] == 0; }
EOF
	changequote([,])dnl
	AC_CHECKING([for gcc warning options])
	cf_save_CFLAGS="$CFLAGS"
	EXTRA_CFLAGS="-W -Wall"
	for cf_opt in \
		Wbad-function-cast \
		Wcast-align \
		Wcast-qual \
		Winline \
		Wmissing-declarations \
		Wmissing-prototypes \
		Wnested-externs \
		Wpointer-arith \
		Wshadow \
		Wstrict-prototypes
	do
		CFLAGS="$cf_save_CFLAGS $EXTRA_CFLAGS -$cf_opt"
		if AC_TRY_EVAL(ac_compile); then
			test -n "$verbose" && AC_MSG_RESULT(... -$cf_opt)
			EXTRA_CFLAGS="$EXTRA_CFLAGS -$cf_opt"
			test "$cf_opt" = Wcast-qual && EXTRA_CFLAGS="$EXTRA_CFLAGS -DXTSTRINGDEFINES"
		fi
	done
	rm -f conftest*
	CFLAGS="$cf_save_CFLAGS"
fi
AC_SUBST(EXTRA_CFLAGS)
CFLAGS="$CFLAGS $EXTRA_CFLAGS"
])dnl