lib: pull in config.h in some files

If the UCLINUX symbol is being defined by way of config.h, we need to
include that header in order to notice.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/lib/self_exec.c b/lib/self_exec.c
index 4b554cf..06441d3 100644
--- a/lib/self_exec.c
+++ b/lib/self_exec.c
@@ -22,9 +22,12 @@
  * 55 Byward Market Square, 2nd Floor North, Ottawa, ON K1N 9C3, Canada
  */
 
+#define _GNU_SOURCE /* for asprintf */
+
+#include "config.h"
+
 #ifdef UCLINUX
 
-#define _GNU_SOURCE /* for asprintf */
 #include <stdarg.h>
 #include <string.h>
 #include <stdio.h>