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.

Change-Id: Ib0d5755e1eb9adb07d80ef0252f57a5c4c57a425
Signed-off-by: Jim Huang <jserv@0xlab.org>