[X86][MMX] Remove widening experimental flag from MMX tests.

Turns out that after the past MMX commits, we don't need to rely on this
flag to get better codegen for MMX. Also update the tests to become
triple neutral.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230637 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed