Pullup from HEAD:
Make GCC define __ARM_PCS and __ARM_PCS_VFP as defined by the ARM C Language
Extentions (clang already defines them):
__ARM_PCS is defined to 1 if the default procedure calling standard for
the translation unit conforms to the "base PCS" defined in [AAPCS].
__ARM_PCS_VFP is defined to 1 if the default is to pass floating-point
parameters in hardware floating-point registers using the "VFP variant PCS"
defined in [AAPCS].