Extend TH with addModCStub

inline-c could benefit of the ability to tell the compiler to include some code in the object file of the current module. https://github.com/fpco/inline-c/issues/21

This way, a module FFI.hs using inline-c doesn't need to produce a file FFI.c with C code, but the code can be built and included in the object file of the module.

For this sake, it would be needed the following TH function:

addModCStub :: String -> Q ()

which would indicate to the compiler that the C code in the given string needs to be built and included in the object file of the current module.