Add `pthread.h` Inclusion if `HAVE_PTHREADS_PF` is defined

Single-case tested with success on Windows 11 with MinGW-w64 Standalone GCC v13.1.0 while building OpenCV 4.7.0

modules/core/src/parallel.cpp

@@ -118,6 +118,8 @@
     #include <ppltasks.h>
 #elif defined HAVE_CONCURRENCY
     #include <ppl.h>
+#elif defined HAVE_PTHREADS_PF
+    #include <pthread.h>
 #endif