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".