Update warnings.m4

* m4/warnings.m4: Update from gnulib.

m4/warnings.m4

@@ -1,5 +1,5 @@
-# warnings.m4 serial 2
-dnl Copyright (C) 2008, 2009, 2010 Free Software Foundation, Inc.
+# warnings.m4 serial 11
+dnl Copyright (C) 2008-2013 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.
@@ -14,23 +14,66 @@ m4_ifdef([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]).
-AC_DEFUN([gl_WARN_ADD],
-[AS_VAR_PUSHDEF([gl_Warn], [gl_cv_warn_$1])dnl
-AC_CACHE_CHECK([whether compiler handles $1], [gl_Warn], [
-  save_CPPFLAGS="$CPPFLAGS"
-  CPPFLAGS="${CPPFLAGS} $1"
-  AC_PREPROC_IFELSE([AC_LANG_PROGRAM([])],
-                    [AS_VAR_SET([gl_Warn], [yes])],
-                    [AS_VAR_SET([gl_Warn], [no])])
-  CPPFLAGS="$save_CPPFLAGS"
+
+# gl_COMPILER_OPTION_IF(OPTION, [IF-SUPPORTED], [IF-NOT-SUPPORTED],
+#                       [PROGRAM = AC_LANG_PROGRAM()])
+# -----------------------------------------------------------------
+# Check if the compiler supports OPTION when compiling PROGRAM.
+#
+# FIXME: gl_Warn must be used unquoted until we can assume Autoconf
+# 2.64 or newer.
+AC_DEFUN([gl_COMPILER_OPTION_IF],
+[AS_VAR_PUSHDEF([gl_Warn], [gl_cv_warn_[]_AC_LANG_ABBREV[]_$1])dnl
+AS_VAR_PUSHDEF([gl_Flags], [_AC_LANG_PREFIX[]FLAGS])dnl
+AS_LITERAL_IF([$1],
+  [m4_pushdef([gl_Positive], m4_bpatsubst([$1], [^-Wno-], [-W]))],
+  [gl_positive="$1"
+case $gl_positive in
+  -Wno-*) gl_positive=-W`expr "X$gl_positive" : 'X-Wno-\(.*\)'` ;;
+esac
+m4_pushdef([gl_Positive], [$gl_positive])])dnl
+AC_CACHE_CHECK([whether _AC_LANG compiler handles $1], m4_defn([gl_Warn]), [
+  gl_save_compiler_FLAGS="$gl_Flags"
+  gl_AS_VAR_APPEND(m4_defn([gl_Flags]),
+    [" $gl_unknown_warnings_are_errors ]m4_defn([gl_Positive])["])
+  AC_LINK_IFELSE([m4_default([$4], [AC_LANG_PROGRAM([])])],
+                 [AS_VAR_SET(gl_Warn, [yes])],
+                 [AS_VAR_SET(gl_Warn, [no])])
+  gl_Flags="$gl_save_compiler_FLAGS"
 ])
-AS_VAR_PUSHDEF([gl_Flags], m4_if([$2], [], [[WARN_CFLAGS]], [[$2]]))dnl
-AS_VAR_IF([gl_Warn], [yes], [gl_AS_VAR_APPEND([gl_Flags], [" $1"])])
+AS_VAR_IF(gl_Warn, [yes], [$2], [$3])
+m4_popdef([gl_Positive])dnl
 AS_VAR_POPDEF([gl_Flags])dnl
 AS_VAR_POPDEF([gl_Warn])dnl
-m4_ifval([$2], [AS_LITERAL_IF([$2], [AC_SUBST([$2])], [])])dnl
 ])
+
+# gl_UNKNOWN_WARNINGS_ARE_ERRORS
+# ------------------------------
+# Clang doesn't complain about unknown warning options unless one also
+# specifies -Wunknown-warning-option -Werror.  Detect this.
+AC_DEFUN([gl_UNKNOWN_WARNINGS_ARE_ERRORS],
+[gl_COMPILER_OPTION_IF([-Werror -Wunknown-warning-option],
+   [gl_unknown_warnings_are_errors='-Wunknown-warning-option -Werror'],
+   [gl_unknown_warnings_are_errors=])])
+
+# gl_WARN_ADD(OPTION, [VARIABLE = WARN_CFLAGS],
+#             [PROGRAM = AC_LANG_PROGRAM()])
+# ---------------------------------------------
+# Adds parameter to WARN_CFLAGS if the compiler supports it when
+# compiling PROGRAM.  For example, gl_WARN_ADD([-Wparentheses]).
+#
+# If VARIABLE is a variable name, AC_SUBST it.
+AC_DEFUN([gl_WARN_ADD],
+[AC_REQUIRE([gl_UNKNOWN_WARNINGS_ARE_ERRORS])
+gl_COMPILER_OPTION_IF([$1],
+  [gl_AS_VAR_APPEND(m4_if([$2], [], [[WARN_CFLAGS]], [[$2]]), [" $1"])],
+  [],
+  [$3])
+m4_ifval([$2],
+         [AS_LITERAL_IF([$2], [AC_SUBST([$2])])],
+         [AC_SUBST([WARN_CFLAGS])])dnl
+])
+
+# Local Variables:
+# mode: autoconf
+# End: