[X86][AArch64][NFC] Add tests for vector masked merge unfolding

Summary:
This is [[ https://bugs.llvm.org/show_bug.cgi?id=37104 | PR37104 ]].

[[ https://bugs.llvm.org/show_bug.cgi?id=6773 | PR6773 ]] will introduce an IR canonicalization that is likely bad for the end assembly.
Previously, `andps`+`andnps` / `bsl` would be generated. (see `@out`)
Now, they would no longer be generated  (see `@in`).

Differential Revision: https://reviews.llvm.org/D46008

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332903 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed