Most host gcc doesn't support -fcanon-prefix-map right now, so
empty DEBUG_PREFIX_MAP_EXTRA to fix the below build error.
| gcc: error: unrecognized command-line option ‘-fcanon-prefix-map’; did you mean ‘-fmacro-prefix-map=’?
Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
31a08525be