http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57316
--- Comment #14 from Jakub Jelinek <jakub at gcc dot gnu.org> --- I wouldn't call the conditional SYSCALL_SUPPORTED, but SANITIZER_SUPPORTED or so. In the future, the configure could have various other reasons why it should give up on building any sanitizer libraries altogether. Also, supposedly __NR_gettid could be added to the test too.
