Support legacy compiler

Adds support for legacy compiler
gcc-linaro-4.9-2015.02-3-x86_64_arm-linux-gnueabihf

To compile using this compiler instead on ARMv7 systems supply
COMPILE_LEGACY=y to make.

Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>