Makefile: Disable undefined-optimized and add -fno-builtin

Suppress the SDLLVM specific compiler warning (undefined optimized)
for the compilation to pass. Also add -fno-builtin such that the
build doesn't pickup any compiler provided built-in functions.

Change-Id: I9507600a9286ec6aff42160d2d77733594b891de
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>