ubsanitizer does not respect file-prefix-map in messages

[apache-hb]

When compiling with -fsanitize=undefined the error messages do not reflect -ffile-prefix-map.
reproducer

where am i? '/beep/example.cpp'
/app/example.cpp:14:5: runtime error: store to null pointer of type 'int'
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /app/example.cpp:14:5 

lines 2 and 3 should contain /beep/example.cpp rather than /app/example.cpp