LibC: Add alloca.h

userspace/libraries/LibC/include/alloca.h

@@ -0,0 +1,14 @@
+#ifndef _ALLOCA_H
+#define _ALLOCA_H 1
+
+// https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/stdio.h.html
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+#define alloca __builtin_alloca
+
+__END_DECLS
+
+#endif