https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58909
--- Comment #15 from Jonathan Wakely <redi at gcc dot gnu.org> --- And the static libc++.a doesn't use weak symbols, so you need to link to libpthread youself, and the necessary symbols get pulled in correctly. The problem for libstdc++.a is that the weak symbols do not cause the libpthread.a symbols to get linked into the binary.
