[CodeGen] add tests for __builtin_sqrt*; NFC
[CodeGen] add tests for __builtin_sqrt*; NFC

I don't know if this is correct, but this is what we currently do.
More discussion in PR27108 and PR27435 and D27618.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@316250 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang