Commit 0b7123f41d regressed the
`include_path` option of ConfigHeader which is intended to set the path,
including subdirectories, that C code would pass to an include
directive.
For example if it passes
.include_path = "config/config.h",
Then the C code should be able to have
#include "config/config.h"
This regressed https://github.com/andrewrk/nasm/ but this commit fixes
it.
fbb38a7682