Synthesize missing register class intersections.

The function TRI::getCommonSubClass(A, B) returns the largest common
sub-class of the register classes A and B.  This patch teaches TableGen
to synthesize sub-classes such that the answer is always maximal.

In other words, every register that is in both A and B will also be
present in getCommonSubClass(A, B).

This introduces these synthetic register classes:

ARM:
    GPRnopc_and_hGPR
    GPRnopc_and_hGPR
    hGPR_and_rGPR
    GPRnopc_and_hGPR
    GPRnopc_and_hGPR
    hGPR_and_rGPR
    tGPR_and_tcGPR
    hGPR_and_tcGPR

X86:
    GR32_NOAX_and_GR32_NOSP
    GR32_NOAX_and_GR32_NOREX
    GR64_NOSP_and_GR64_TC
    GR64_NOSP_and_GR64_TC
    GR64_NOREX_and_GR64_TC
    GR32_NOAX_and_GR32_NOSP
    GR32_NOAX_and_GR32_NOREX
    GR32_NOAX_and_GR32_NOREX_NOSP
    GR64_NOSP_and_GR64_TC
    GR64_NOREX_and_GR64_TC
    GR64_NOREX_NOSP_and_GR64_TC
    GR32_NOAX_and_GR32_NOSP
    GR32_NOAX_and_GR32_NOREX
    GR32_NOAX_and_GR32_NOREX_NOSP
    GR32_ABCD_and_GR32_NOAX
    GR32_NOAX_and_GR32_NOSP
    GR32_NOAX_and_GR32_NOREX
    GR32_NOAX_and_GR32_NOREX_NOSP
    GR32_ABCD_and_GR32_NOAX
    GR32_NOAX_and_GR32_TC
    GR32_NOAX_and_GR32_NOSP
    GR64_NOSP_and_GR64_TC
    GR32_NOAX_and_GR32_NOREX
    GR32_NOAX_and_GR32_NOREX_NOSP
    GR64_NOREX_and_GR64_TC
    GR64_NOREX_NOSP_and_GR64_TC
    GR32_ABCD_and_GR32_NOAX
    GR64_ABCD_and_GR64_TC
    GR32_NOAX_and_GR32_TC
    GR32_AD_and_GR32_NOAX

Other targets are unaffected.

llvm-svn: 146657