Add libm_hard.a for armeabi-v7a

A math library compiled with -mhard-float.  Build instructions:

1. cd to a recent Android source tree: bionic.git
   fbefb252b09634114977dbd1b48dd42bb2629b83 (internal) in this case
2. Temporarily remove "-mfloat-abi=softfp" from build/core/combo/arch/arm/armv7*
   and build/core/combo/TARGET_linux-arm.mk
3. Temporarily add "-mhard-float -mfloat-abi=hard" to LOCAL_CFLAGS
   for libm.a in bionic/libm/Android.mk
4. make -B -j32 out/target/product/generic/obj/STATIC_LIBRARIES/libm_intermediates/libm.a
5. Rename it

Change-Id: I107eea48af75e97b448862cfc7aae2e8f8911a63

Author: Andrew Hsieh