[ConstantFolding] Refactor math functions to use LLVM ones (NFC)
[ConstantFolding] Refactor math functions to use LLVM ones (NFC)

When possible, replace calls to library routines on the host with equivalent
ones in LLVM.

Differential revision: https://reviews.llvm.org/D67459

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@371677 91177308-0d34-0410-b5e6-96231b3b80d8

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