[X86] Add a AVX512VBMI command line to min-legal-vector-width.ll. Always enable fast-variable-shuffle
[X86] Add a AVX512VBMI command line to min-legal-vector-width.ll. Always enable fast-variable-shuffle

Trying to minimize the features we need to manipulate when this
is updated for D67259.

The VBMI is interesting because it enables some improved combining
for truncates.

I enabled fast-variable-shuffle because all the CPUs we're going
to add implicitly enable it. So they can share check lines.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@371261 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm