Add alloca.h.

libc/include/alloca.h

@@ -0,0 +1,51 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    The Sortix C Library 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 Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    alloca.h
+    Stack-based memory allocation.
+
+*******************************************************************************/
+
+#ifndef INCLUDE_ALLOCA_H
+#define INCLUDE_ALLOCA_H
+
+#include <features.h>
+
+__BEGIN_DECLS
+
+@include(size_t.h)
+
+/* If somehow another declaration of alloca happened. This shouldn't happen, but
+   glibc does this and we might as well do it also. */
+#undef alloca
+
+/* Declare a function prototype despite that there really is no alloca function
+   in Sortix. The compiler will normally be run with -fbuiltin and simply use
+   the compiler builtin as intended. */
+void* alloca(size_t);
+
+/* In case the compilation is run with -fno-builtin, we'll call the builtin
+   function directly, since there is no alloca function in the first place. You
+   can simply undef this if you want the real prototype, which will give a link
+   error if -fno-builtin is passed. */
+#define alloca(size) __builtin_alloca(size)
+
+__END_DECLS
+
+#endif