AMDGPUPrintfRuntimeBindingPass is not run in the IR optimization
pipeline with -O0.
This means that with OpenCL the printf definition coming from
device_libs gets linked with the user's code, which blocks
AMDGPUPrintfRuntimeBindingPass from working after the linkage is done.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D146720
