According to the 2nd point on [1], -lregex is required on QNX. [1] https://www.qnx.com/developers/docs/7.1/#com.qnx.doc.ide.userguide/topic/writing_test_programs.html
On QNX, pthread is part of libc [1]. There's no separate pthread library to link. [1] https://www.qnx.com/developers/docs/7.1/index.html#com.qnx.doc.neutrino.lib_ref/topic/p/pthread_create.html