Move some utility TableGen defs, classes, etc. into a common file so
they may be used my multiple pattern files. We will use this for
the AVX specification to help with the transition from the current
SSE specification.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95727 91177308-0d34-0410-b5e6-96231b3b80d8