configure: new option --enable-gcc-warnings

I have been using this change for many months in my private copy
of Emacs, and have used it to find several bugs.  It's mature
enough to publish now.
* Makefile.in (GNULIB_MODULES): Add warnings, manywarnings.
* configure.in: Support --enable-gcc-warnings, in the style of
other GNU packages such as coreutils.
(C_WARNINGS_SWITCH): Remove, replacing with...
(WARN_CFLAGS, GNULIB_WARN_CFLAGS): New variable.
(PKG_CHECK_MODULES, C_SWITCH_X_SITE): Use -isystem rather than -I,
when including system files with GCC.
* etc/NEWS: Mention --enable-gcc-warnings.
* lib/Makefile.am (AM_CFLAGS): New macro.
* m4/manywarnings.m4, m4/warnings.m4: New files, from gnulib.
* lib-src/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(BASE_CFLAGS): Use new macros rather than old.
* lwlib/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(ALL_CFLAGS): Use new macros rather than old.
* oldXMenu/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(ALL_CFLAGS): Use new macros rather than old.
* src/Makefile.in (C_WARNINGS_SWITCH): Remove.
(WARN_CFLAGS, WERROR_CFLAGS): New macros.
(ALL_CFLAGS): Use new macros rather than old.
* src/process.c: Ignore -Wstrict-overflow to work around GCC bug 52904.
* src/regex.c: Ignore -Wstrict-overflow.  If !emacs, also ignore
-Wunused-but-set-variable, -Wunused-function, -Wunused-macros,
-Wunused-result, -Wunused-variable.  This should go away once
the Emacs and Gnulib regex code is merged.
(xmalloc, xrealloc): Now static.

1 files changed, 42 insertions, 0 deletions

diff --git a/m4/warnings.m4 b/m4/warnings.m4
new file mode 100644
index 0000000000..c14c4801e7
--- /dev/null
+++ b/m4/warnings.m4
@@ -0,0 +1,42 @@
+# warnings.m4 serial 6
+dnl Copyright (C) 2008-2012 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl From Simon Josefsson
+
+# gl_AS_VAR_APPEND(VAR, VALUE)
+# ----------------------------
+# Provide the functionality of AS_VAR_APPEND if Autoconf does not have it.
+m4_ifdef([AS_VAR_APPEND],
+[m4_copy([AS_VAR_APPEND], [gl_AS_VAR_APPEND])],
+[m4_define([gl_AS_VAR_APPEND],
+[AS_VAR_SET([$1], [AS_VAR_GET([$1])$2])])])
+
+
+# gl_WARN_ADD(PARAMETER, [VARIABLE = WARN_CFLAGS])
+# ------------------------------------------------
+# Adds parameter to WARN_CFLAGS if the compiler supports it.  For example,
+# gl_WARN_ADD([-Wparentheses]).
+#
+# If VARIABLE is a variable name, AC_SUBST it.
+AC_DEFUN([gl_WARN_ADD],
+dnl FIXME: gl_Warn must be used unquoted until we can assume
+dnl autoconf 2.64 or newer.
+[AS_VAR_PUSHDEF([gl_Warn], [gl_cv_warn_[]_AC_LANG_ABBREV[]_$1])dnl
+AS_VAR_PUSHDEF([gl_Flags], [_AC_LANG_PREFIX[]FLAGS])dnl
+AC_CACHE_CHECK([whether _AC_LANG compiler handles $1], m4_defn([gl_Warn]), [
+  gl_save_compiler_FLAGS="$gl_Flags"
+  gl_Flags="$gl_Flags $1"
+  AC_COMPILE_IFELSE([AC_LANG_PROGRAM([])],
+                    [AS_VAR_SET(gl_Warn, [yes])],
+                    [AS_VAR_SET(gl_Warn, [no])])
+  gl_Flags="$gl_save_compiler_FLAGS"
+])
+AS_VAR_IF(gl_Warn, [yes],
+  [gl_AS_VAR_APPEND(m4_if([$2], [], [[WARN_CFLAGS]], [[$2]]), [" $1"])])
+AS_VAR_POPDEF([gl_Flags])dnl
+AS_VAR_POPDEF([gl_Warn])dnl
+m4_ifval([$2], [AS_LITERAL_IF([$2], [AC_SUBST([$2])], [])])dnl
+])