Added m4 scripts to check compiler flags

m4/.cvsignore

@@ -0,0 +1,3 @@
+*.m4
+Makefile
+Makefile.in

m4/Makefile.am

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+
+EXTRA_DIST = compiler-flags.m4
+

m4/compiler-flags.m4

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+# serial 3
+# Find valid warning flags for the C Compiler.           -*-Autoconf-*-
+#
+# Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301  USA
+
+# Written by Jesse Thilo.
+
+AC_DEFUN([gl_COMPILER_FLAGS],
+  [AC_MSG_CHECKING(whether compiler accepts $1)
+   AC_SUBST(COMPILER_FLAGS)
+   ac_save_CFLAGS="$CFLAGS"
+   CFLAGS="$CFLAGS $1"
+   AC_TRY_COMPILE(,
+    [int x;],
+    COMPILER_FLAGS="$COMPILER_FLAGS $1"
+    AC_MSG_RESULT(yes),
+    AC_MSG_RESULT(no))
+  CFLAGS="$ac_save_CFLAGS"
+ ])