DragonFlyBSD

Stub pthread_cancel symbol in libc causes certain issues with gcc, specially with libgcc.so and libgfortran.so in gcc7 (likely other libs or utilities too, that define dummy weak pthread_cancel symbol to check if it gets claimed by anything).

So far in installed world with attached patch I didn't noticed any breakage in dports or base. gcc50 still has:
[rw@_ zsrc]$ readelf -s /usr/libexec/gcc50/gcc |grep pthread
4: 0000000000000000 0 FUNC WEAK DEFAULT UND pthread_mutex_unlock@DF404.0 (2)
6: 0000000000000000 0 FUNC WEAK DEFAULT UND pthread_once@DF404.0 (2)
30: 0000000000000000 0 FUNC WEAK DEFAULT UND pthread_mutex_lock@DF404.0 (2)
120: 0000000000000000 0 NOTYPE WEAK DEFAULT UND pthread_cancel