env: re-add support for auto-completion

Currently, only basic completion is supported (no globs), but this is
what we had previously.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/common.h b/include/common.h
index 0d1c872..d8c912d 100644
--- a/include/common.h
+++ b/include/common.h
@@ -632,6 +632,7 @@
 /* lib/qsort.c */
 void qsort(void *base, size_t nmemb, size_t size,
 	   int(*compar)(const void *, const void *));
+int strcmp_compar(const void *, const void *);
 
 /* lib/time.c */
 void	udelay        (unsigned long);