Perform blas_thread_shutdown with pthread_atfork() on Cygwin

Even if we're directly using the win32 threading driver and not pthreads,
pthread_atfork still works fine to register a pre-fork handler, and is
necessary to restore the threading server to a pre-initialized state.

driver/others/blas_server_win32.c

@@ -40,6 +40,14 @@
 #include <stdlib.h>
 #include "common.h"
 
+#if defined(OS_CYGWIN_NT) && !defined(unlikely)
+#ifdef __GNUC__
+#define unlikely(x) __builtin_expect(!!(x), 0)
+#else
+#define unlikely(x) (x)
+#endif
+#endif
+
 /* This is a thread implementation for Win32 lazy implementation */
 
 /* Thread server common infomation */
@@ -53,7 +61,7 @@ typedef struct{
 
 } blas_pool_t;
 
-/* We need this grobal for cheking if initialization is finished.   */
+/* We need this global for cheking if initialization is finished.   */
 int blas_server_avail = 0;
 
 /* Local Variables */
@@ -340,6 +348,11 @@ int blas_thread_init(void){
 
 int exec_blas_async(BLASLONG pos, blas_queue_t *queue){
 
+#if defined(SMP_SERVER) && defined(OS_CYGWIN_NT)
+  // Handle lazy re-init of the thread-pool after a POSIX fork
+  if (unlikely(blas_server_avail == 0)) blas_thread_init();
+#endif
+
   blas_queue_t *current;
 
   current = queue;
@@ -405,6 +418,11 @@ int exec_blas_async_wait(BLASLONG num, blas_queue_t *queue){
 /* Execute Threads */
 int exec_blas(BLASLONG num, blas_queue_t *queue){
 
+#if defined(SMP_SERVER) && defined(OS_CYGWIN_NT)
+  // Handle lazy re-init of the thread-pool after a POSIX fork
+  if (unlikely(blas_server_avail == 0)) blas_thread_init();
+#endif
+
 #ifndef ALL_THREADED
    int (*routine)(blas_arg_t *, void *, void *, double *, double *, BLASLONG);
 #endif

driver/others/memory.c

@@ -323,7 +323,7 @@ void openblas_fork_handler()
   //   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60035
   // In the mean time build with USE_OPENMP=0 or link against another
   // implementation of OpenMP.
-#if !(defined(OS_WINDOWS) || defined(OS_ANDROID)) && defined(SMP_SERVER)
+#if !((defined(OS_WINDOWS) && !defined(OS_CYGWIN_NT)) || defined(OS_ANDROID)) && defined(SMP_SERVER)
   int err;
   err = pthread_atfork ((void (*)(void)) BLASFUNC(blas_thread_shutdown), NULL, NULL);
   if(err != 0)