pthread_sigmask() detected incorrectly on MinGW by configure

[Pavel Fedin]

 Hello! I have found one more problem with GNULib on Windows.

 This time it concerns pthread_sigmask(). configure script detects it as
present, and this is technically correct, but:
--- cut ---
/* Windows has rudimentary signals support.  */
#define pthread_sigmask(H, S1, S2) 0
--- cut ---
 (see
http://sourceforge.net/p/mingw-w64/mingw-w64/ci/master/tree/mingw-w64-librar
ies/winpthreads/include/pthread_signal.h)

 So, this is actually incorrect. And this causes failure building gnulib's
pthread_sigmask.c, because it tries to refer original pthread_sigmask()
after #undef'ing it. Of course this causes "undefined symbol" while linking.
 I would suggest that configure script just knows that on *-mingw* systems
pthread_sigmask is not present. An alternate way to fix this is to add to
the .c file:
--- cut ---
#ifdef _WIN32
#undef HAVE_PTHREAD_SIGMASK
#endif
--- cut ---

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia