Change how we handle alloca to conform with how it is suggested in the autoconf manual for AC_FUNC_ALLOCA. FreeBSD 6 now builds again and no other platforms should be broken by this.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@89396 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/compat.h

@@ -52,9 +52,14 @@
 #endif
 
 #ifdef HAVE_ALLOCA_H
-#include <alloca.h>	/* not necessarily present - could be in stdlib */
-#elif defined(HAVE_ALLOCA)
-#include <malloc.h>	/* see if it is here... */
+#include <alloca.h>
+#elif defined(__GNUC__)
+#define alloca __builtin_alloca
+#elif defined(_AIX)
+#define alloca __alloca
+#elif defined(_MSC_VER)
+#include <malloc.h>
+#define alloca _alloca
 #endif
 
 #include <stdio.h>	/* this is always present */