Optimize __memset_chk, __memcpy_chk. DO NOT MERGE.

This change creates assembler versions of __memcpy_chk/__memset_chk
that is implemented in the memcpy/memset assembler code. This change
avoids an extra call to memcpy/memset, instead allowing a simple fall
through to occur from the chk code into the body of the real
implementation.

Testing:

- Ran the libc_test on __memcpy_chk/__memset_chk on all nexus devices.
- Wrote a small test executable that has three calls to __memcpy_chk and
  three calls to __memset_chk. First call dest_len is length + 1. Second
  call dest_len is length. Third call dest_len is length - 1.
  Verified that the first two calls pass, and the third fails. Examined
  the logcat output on all nexus devices to verify that the fortify
  error message was sent properly.
- I benchmarked the new __memcpy_chk and __memset_chk on all systems. For
  __memcpy_chk and large copies, the savings is relatively small (about 1%).
  For small copies, the savings is large on cortex-a15/krait devices
  (between 5% to 30%).
  For cortex-a9 and small copies, the speed up is present, but relatively
  small (about 3% to 5%).
  For __memset_chk and large copies, the savings is also small (about 1%).
  However, all processors show larger speed-ups on small copies (about 30% to
  100%).

Bug: 9293744

Merge from internal master.

(cherry-picked from 7c860db074)

Change-Id: I916ad305e4001269460ca6ebd38aaa0be8ac7f52

libc/arch-arm/arm.mk

@@ -26,6 +26,15 @@ _LIBC_ARCH_STATIC_SRC_FILES := \
 _LIBC_ARCH_DYNAMIC_SRC_FILES := \
     arch-arm/bionic/exidx_dynamic.c
 
+# Remove the C++ fortify function implementations for which there is an
+# arm assembler version.
+_LIBC_FORTIFY_FILES_TO_REMOVE := \
+    bionic/__memcpy_chk.cpp \
+    bionic/__memset_chk.cpp \
+
+libc_common_src_files := \
+    $(filter-out $(_LIBC_FORTIFY_FILES_TO_REMOVE),$(libc_common_src_files))
+
 ifeq ($(strip $(wildcard bionic/libc/arch-arm/$(TARGET_CPU_VARIANT)/$(TARGET_CPU_VARIANT).mk)),)
 $(error "TARGET_CPU_VARIANT not set or set to an unknown value. Possible values are cortex-a7, cortex-a8, cortex-a9, cortex-a15, krait. Use generic for devices that do not have a CPU similar to any of the supported cpu variants.")
 endif