[NFC][InstCombine] Add srem-by-signbit tests - still can fold to bittest
[NFC][InstCombine] Add srem-by-signbit tests - still can fold to bittest

https://rise4fun.com/Alive/IIeS

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@366642 91177308-0d34-0410-b5e6-96231b3b80d8

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