[AArch64][x86] add tests for pow(x, 0.25); NFC

Folds for this were proposed in D49306, but we
decided the transform is better suited for the backend.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341341 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed