Configure: Added check for compiler attribute 'noreturn'

This attribute for functions was not standard until recently, so
there are a few different possible syntax. With this patch, the
configure script will search for the proper syntax, and define what
is needed to have the attribute compile correctly.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

configure.ac

@@ -247,6 +247,7 @@ dnl ==============================================================
 AC_DECL_SYS_SIGLIST
 AC_C_CONST
 AC_C_INLINE
+WM_C_NORETURN
 AC_TYPE_SIZE_T
 AC_TYPE_PID_T
 AC_TYPE_SIGNAL

m4/wm_attributes.m4

@@ -0,0 +1,92 @@
+# wm_attributes.m4 - Macros to check compiler attributes and define macros
+#
+# Copyright (c) 2013 Christophe Curis
+#
+# 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.
+
+# WM_C_NORETURN
+# -------------
+#
+# Checks if the compiler supports ISO C11 noreturn attribute, if not
+# try to define the keyword to a known syntax that does the job, or
+# if nothing works sets it to empty to, at least, be able to
+# compile the sources
+AC_DEFUN_ONCE([WM_C_NORETURN],
+[AC_REQUIRE([_WM_SHELLFN_FUNCATTR])
+AC_CACHE_CHECK([for noreturn], [wm_cv_c_noreturn],
+    [wm_cv_c_noreturn=no
+     AC_COMPILE_IFELSE(
+      [AC_LANG_PROGRAM(
+          [#include <unistd.h>
+#include <stdnoreturn.h>
+
+/* Attribute in the prototype of the function */
+noreturn int test_function(void);
+
+/* Attribute on the function itself */
+noreturn int test_function(void) {
+  _exit(1);
+}
+], [  test_function();])],
+          [wm_cv_c_noreturn=stdnoreturn],
+          [for wm_attr in  dnl
+             "__attribute__((noreturn))"   dnl for modern GCC-like compilers
+             "__attribute__((__noreturn__))"   dnl for older GCC-like compilers
+             "__declspec(noreturn)"   dnl for some other compilers
+           ; do
+             AS_IF([wm_fn_c_try_compile_funcattr "$wm_attr"],
+                 [wm_cv_c_noreturn="$wm_attr" ; break])
+           done]) dnl
+    ])
+AS_CASE([$wm_cv_c_noreturn],
+    [stdnoreturn],
+        [AC_DEFINE([HAVE_STDNORETURN], 1,
+            [Defined if header "stdnoreturn.h" exists, it defines ISO C11 attribute 'noreturn' and it works])],
+    [no],
+        [AC_DEFINE([noreturn], [],
+            [Defines the attribute to tell the compiler that a function never returns, if the ISO C11 attribute does not work])],
+    [AC_DEFINE_UNQUOTED([noreturn], [${wm_cv_c_noreturn}],
+        [Defines the attribute to tell the compiler that a function never returns, if the ISO C11 attribute does not work])])
+])
+
+# _WM_SHELLFN_FUNCATTRIBUTE
+# ----------------------
+# (internal shell function only!)
+#
+# Create a shell function to check if we can compile with special
+# function attributes
+AC_DEFUN([_WM_SHELLFN_FUNCATTR],
+[@%:@ wm_fn_c_try_compile_funcattr ATTRIBUTE
+@%:@ ---------------------------------------
+@%:@ Try compiling a function with the attribute ATTRIBUTE
+wm_fn_c_try_compile_funcattr ()
+{
+  AC_COMPILE_IFELSE(
+      [AC_LANG_PROGRAM(
+          [
+/* Attribute in the prototype of the function */
+int test_function(int arg) $[]1;
+
+/* Attribute on the function itself */
+$[]1 int test_function(int arg) {
+  return arg - 1;
+}], [int val;
+val = test_function(1);
+return val;])],
+      [wm_retval=0],
+      [wm_retval=1])
+  AS_SET_STATUS([$wm_retval])
+}
+])