GNU libc on GNU/Hurd doesn't define `__SIGRTMIN'. From . --- a/libgcc/generic-morestack.c 2011-12-19 21:14:52.000000000 +0100 +++ b/libgcc/generic-morestack.c 2011-12-19 21:15:35.000000000 +0100 @@ -507,7 +507,7 @@ sigemptyset (&__morestack_initial_sp.mask); sigfillset (&__morestack_fullmask); -#ifdef __GLIBC__ +#if defined(__GLIBC__) && defined(__SIGRTMIN) /* In glibc, the first two real time signals are used by the NPTL threading library. By taking them out of the set of signals, we avoiding copying the signal mask in pthread_sigmask. More