[Bug gcov-profile/67937] gcov gives wrong results when negative counts are involved

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67937

--- Comment #6 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
We can have negative counters on fake edges in case the code uses abnormal
edges that we can't instrument correctly.  setjmp/longjmp is one of examples. 
If you profile kernel, you will have inconsistencies in profile because of race
conditions.