[HIP][AMDGPU] expand printf when compiling HIP to AMDGPU

Summary:
This change implements the expansion in two parts:
- Add a utility function emitAMDGPUPrintfCall() in LLVM.
- Invoke the above function from Clang CodeGen, when processing a HIP
  program for the AMDGPU target.

The printf expansion has undefined behaviour if the format string is
not a compile-time constant. As a sufficient condition, the HIP
ToolChain now emits -Werror=format-nonliteral.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D71365