In this patch, we create a new ModulePass that mimics the LinkInModules
API from CodeGenAction.cpp, and a new command line option to enable the
pass. As part of the implementation, we needed to refactor the
BackendConsumer class definition into a new separate header (instead of
embedded in CodeGenAction.cpp). With this new pass, we can now re-link
bitcodes supplied via the -mlink-built-in bitcodes as part of the
RunOptimizationPipeline.
With the re-linking pass, we now handle cases where new device library
functions are introduced as part of the optimization pipeline.
Previously, these newly introduced functions (for example a fused sincos
call) would result in a linking error due to a missing function
definition. This new pass can be initiated via:
-mllvm -relink-builtin-bitcode-postop
Also note we intentionally exclude bitcodes supplied via the
-mlink-bitcode-file option from the second linking step
