Export XSI sigpause

There are two common sigpause variants, both of which take an int argument.
If you request _XOPEN_SOURCE or _GNU_SOURCE, you get the System V version,
which removes the given signal from the process's signal mask; otherwise
you get the BSD version, which sets the process's signal mask to the given
value.

Signed-off-by: Yaakov Selkowitz <yselkowi@redhat.com>

winsup/cygwin/common.din

@@ -102,6 +102,7 @@ __wrap__ZdlPv NOSIGFE               # void operator delete(void *p) throw()
 __wrap__ZdlPvRKSt9nothrow_t NOSIGFE # void operator delete(void *p, const std::nothrow_t &nt) throw()
 __xdrrec_getrec SIGFE
 __xdrrec_setnonblock SIGFE
+__xpg_sigpause SIGFE
 __xpg_strerror_r SIGFE
 _exit SIGFE
 _feinitialise NOSIGFE