[PATCH android/bionic] Add ARM optimized strcmp()

Reference results of the experiments on TI OMAP3430 at 600 MHz

$ bench_strcmp -N "strcmp_1k" -s 1k -I 200

[original C code] prc thr usecs/call samples errors cnt/samp size strcmp_1k 1 1 10.38000 102 0 15000 1024

[ARM optimized code] prc thr usecs/call samples errors cnt/samp size strcmp_1k 1 1 3.08840 88 0 15000 1024

The work was derived from ARM Ltd, contributed to newlib, and reworked for Android by Linaro.

Code Review: https://review.source.android.com/#change,22419