Move <string.h> inclusion to compiler.h

There is absolutely no reason not to include <string.h> globally, and
with the inline function for mempcpy() we need it there anyway.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

include/compiler.h

@@ -82,6 +82,7 @@
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <limits.h>
 
 #ifdef HAVE_SYS_TYPES_H