Added #include <string.h> to memmove.c, memcpy.c and strcat.c

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@17285 a1c6a512-1295-4272-9138-f99709370657
diff --git a/firmware/common/strcat.c b/firmware/common/strcat.c
index e3366d7..2215295 100644
--- a/firmware/common/strcat.c
+++ b/firmware/common/strcat.c
@@ -1,3 +1,5 @@
+#include <string.h>
+
 char *strcat(char *s1,
              const char *s2)
 {