Allow GCC-built fortified code to run on a clang-built bionic.

Even though code built with clang won't be fully fortified
and won't contain calls to our various helpers, binaries built
with GCC will.

Change-Id: I389b2f1e22a3e89b22aadedc46397bf704f9ca79
Fix backwards compatible system property structure

The original structure included four reserved 32-bit values. This
change adds these back into the structure so that the
__system_property_find_compat function will (again) process the system
properties correctly.
Allocate additional space on stack for indirect syscall

The caller is only required to allocate 16 bytes on the
stack for a0-a3. syscall is handling up to 6 arguments so
additional space is needed on the stack to avoid corrupting the
callers frame.

Change-Id: I054b31696decc3e17d9c70af18cd278b852235d1

Conflicts:
	libc/arch-mips/bionic/syscall.S