Clean up <stdlib.h> slightly.

Interestingly, this mostly involves cleaning up our implementation of
various <string.h> functions.

Change-Id: Ifaef49b5cb997134f7bc0cc31bdac844bdb9e089
diff --git a/libc/arch-arm/krait/krait.mk b/libc/arch-arm/krait/krait.mk
index 450f472..8bd5e8b 100644
--- a/libc/arch-arm/krait/krait.mk
+++ b/libc/arch-arm/krait/krait.mk
@@ -12,4 +12,6 @@
     arch-arm/cortex-a15/bionic/strcat.S \
     arch-arm/cortex-a15/bionic/strcpy.S \
     arch-arm/cortex-a15/bionic/strlen.S \
-    bionic/memmove.c \
+
+libc_openbsd_src_files_arm += \
+    upstream-openbsd/lib/libc/string/memmove.c \