Sorry for the pedantry, but: I read the title of this bug as wanting these two values to be the exact same pointer. If you're talking about putting a constant string in a header file, you'll get an (identical) copy of that string in every .o that references it (unless your linker collapses identical strings, which I don't know if they do).
From the description, it sounds like you want them to merely be guaranteed identical strings, but they don't have to be the same exact pointer.
tl;dr: do you mean "=="? the title implies you mean "is".