Fix data race in bugReportStart (#7700)
Fix data race in bugReportStart (#7700)

The previous fix using _Atomic was insufficient, since we check and set it in
different places.

The implications of this bug are just that a portion of the bug report will be shown
twice, in the race case of two concurrent crashes.
PKRoma/redis,ctripcorp/redis,ofirluzon/redis,yossigo/redis,yossigo/redis,soloestoy/redis,ctripcorp/redis,neomantra/redis,antirez/redis,PKRoma/redis,neomantra/redis,ctripcorp/redis,ofirluzon/redis,ofirluzon/redis,oranagra/redis,PKRoma/redis,charsyam/redis,yossigo/redis,ofirluzon/redis,oranagra/redis,ctripcorp/redis,soloestoy/redis,oranagra/redis,neomantra/redis,yossigo/redis,antirez/redis,ofirluzon/redis,antirez/redis,soloestoy/redis,charsyam/redis,PKRoma/redis,antirez/redis,oranagra/redis,PKRoma/redis,soloestoy/redis,yossigo/redis,charsyam/redis,soloestoy/redis,oranagra/redis,charsyam/redis,neomantra/redis,neomantra/redis,charsyam/redis