[SimplifyCFG] Add "safe abs" test from CMSIS DSP 'abs_with_clamp()'
[SimplifyCFG] Add "safe abs" test from CMSIS DSP 'abs_with_clamp()'

With -phi-node-folding-threshold=3
this branch would get flattened into select.

See https://reviews.llvm.org/D65148#1629010

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@368847 91177308-0d34-0410-b5e6-96231b3b80d8

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