Fix MIPS build.

ARM and x86 have custom memcpy implementations, but MIPS relies on the generic
one, which I recently moved.

Change-Id: I9e49243f63b27a4123f2c6623d6286ec82d333c7
diff --git a/libc/Android.mk b/libc/Android.mk
index 73b8acb..cd44f23 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -479,8 +479,8 @@
 	arch-mips/string/mips_strlen.c
 
 libc_common_src_files += \
+	bionic/memcmp.c \
 	string/bcopy.c \
-	string/memcmp.c \
 	string/strcmp.c \
 	string/strcpy.c \
 	string/strncmp.c