Use Intel CPU flags to determine target supported features.

Summary:
This patch uses the instruction CPUID to verify that FXSAVE, XSAVE, AVX
and MPX are supported by the target hardware. In case the HW supports XSAVE,
and at least one of the extended register sets, it further checks if the
target software has the kernel support for such features, by verifying that
their XSAVE part is correctly managed.

Differential Revision: https://reviews.llvm.org/D24559

llvm-svn: 281507