libgcc_compat: Introduce __aeabi_lasr for cortex-a9 and higher

This is needed when passing -mcpu=cortex-a9 or higher on a modern
toolchain for prebuilt library compatibility

Change-Id: I73eb2393377914ae26216a8c2828ad973d1c1225
Fix abort(3) to raise SIGABRT rather than causing SIGSEGV.

tgkill() needs the .save stack unwinding directive to get the complete
stack trace.

BUG: https://code.google.com/p/android/issues/detail?id=16672

Change-Id: Ifb447dca2147a592c48baf32769dfc175d8aea72