Backport fix for Bug#6170 from trunk.

Fix alloca definition when using gcc on non-gnu systems.
* configure.in: Use the code sequence indicated by "info autoconf"
for alloca (bug#6170).

ChangeLog

+2010-11-13  Dan Nicolaescu  <dann@ics.uci.edu>
+
+	Fix alloca definition when using gcc on non-gnu systems.
+	* configure.in: Use the code sequence indicated by "info autoconf"
+	for alloca (bug#6170).
+
 2010-11-08  Stefan Monnier  <monnier@iro.umontreal.ca>
 
 	* .dir-locals.el (log-edit-mode): Set log-edit-rewrite-fixes.

configure.in

@@ -2927,15 +2927,19 @@ extern char *getenv ();
 #ifdef HAVE_STDLIB_H
 #include <stdlib.h>
 #endif
-#ifndef __GNUC__
-# ifdef HAVE_ALLOCA_H
-#  include <alloca.h>
-# else /* AIX files deal with #pragma.  */
-#  ifndef alloca /* predefined by HP cc +Olibcalls */
-char *alloca ();
-#  endif
-# endif /* HAVE_ALLOCA_H */
-#endif /* __GNUC__ */
+#ifdef HAVE_ALLOCA_H
+# include <alloca.h>
+#elif defined __GNUC__
+# define alloca __builtin_alloca
+#elif defined _AIX
+# define alloca __alloca
+#else
+# include <stddef.h>
+# ifdef  __cplusplus
+extern "C"
+# endif
+void *alloca (size_t);
+#endif
 #ifndef HAVE_SIZE_T
 typedef unsigned size_t;
 #endif

src/config.in

@@ -1178,15 +1178,19 @@ extern char *getenv ();
 #ifdef HAVE_STDLIB_H
 #include <stdlib.h>
 #endif
-#ifndef __GNUC__
-# ifdef HAVE_ALLOCA_H
-#  include <alloca.h>
-# else /* AIX files deal with #pragma.  */
-#  ifndef alloca /* predefined by HP cc +Olibcalls */
-char *alloca ();
-#  endif
-# endif /* HAVE_ALLOCA_H */
-#endif /* __GNUC__ */
+#ifdef HAVE_ALLOCA_H
+# include <alloca.h>
+#elif defined __GNUC__
+# define alloca __builtin_alloca
+#elif defined _AIX
+# define alloca __alloca
+#else
+# include <stddef.h>
+# ifdef  __cplusplus
+extern "C"
+# endif
+void *alloca (size_t);
+#endif
 #ifndef HAVE_SIZE_T
 typedef unsigned size_t;
 #endif