Fix memchr overflow.

The overflow's actually in the generic C implementation of memchr.

While I'm here, let's switch our generic memrchr to the OpenBSD version too.

Bug: https://code.google.com/p/android/issues/detail?id=147048
Change-Id: I296ae06a1ee196d2c77c95a22f11ee4d658962da
diff --git a/libc/arch-mips/mips.mk b/libc/arch-mips/mips.mk
index 7e3fe25..33eceab 100644
--- a/libc/arch-mips/mips.mk
+++ b/libc/arch-mips/mips.mk
@@ -10,8 +10,6 @@
     bionic/__memset_chk.cpp \
     bionic/__strcpy_chk.cpp \
     bionic/__strcat_chk.cpp \
-    bionic/memchr.c \
-    bionic/memrchr.c \
     bionic/strchr.cpp \
     bionic/strnlen.c \
     bionic/strrchr.cpp \
@@ -27,7 +25,9 @@
     upstream-freebsd/lib/libc/string/wmemmove.c \
 
 libc_openbsd_src_files_mips += \
+    upstream-openbsd/lib/libc/string/memchr.c \
     upstream-openbsd/lib/libc/string/memmove.c \
+    upstream-openbsd/lib/libc/string/memrchr.c \
     upstream-openbsd/lib/libc/string/stpcpy.c \
     upstream-openbsd/lib/libc/string/stpncpy.c \
     upstream-openbsd/lib/libc/string/strcat.c \