Support avx512f in __builtin_cpu_supports.

Support avx512f in __builtin_cpu_supports.

gcc/

        * config/i386/cpuid.h (bit_MPX, bit_BNDREGS, bit_BNDCSR):
        Define.
        * config/i386/i386.c (get_builtin_code_for_version): Add avx512f.
        (fold_builtin_cpu): Ditto.
        * doc/extend.texi: Documment it.

gcc/testsuite/

        * g++.dg/ext/mv2.C: Add test for target ("avx512f").
        * gcc.target/i386/builtin_target.c: Ditto.

libgcc/

        * config/i386/cpuinfo.c (processor_features): Add FEATURE_AVX512F.
        * config/i386/cpuinfo.c (get_available_features): Detect it.

From-SVN: r218125