GCC 8 implements -fmacro-prefix-map. Like -fdebug-prefix-map, it replaces a string prefix for the __FILE__ macro.
-ffile-prefix-map is the union of -fdebug-prefix-map and -fmacro-prefix-map
Reviewed By: rnk, Lekensteyn, maskray
Differential Revision: https://reviews.llvm.org/D49466
Dan McGregor