FindThreads: Fix pthread library check in GHS Multi Generator

Modules/FindThreads.cmake

@@ -161,6 +161,9 @@ if(CMAKE_HAVE_PTHREAD_H)
          _check_pthreads_flag()
       endif ()
 
+      if(CMAKE_SYSTEM MATCHES "GHS-MULTI")
+        _check_threads_lib(posix pthread_create CMAKE_HAVE_PTHREADS_CREATE)
+      endif()
       _check_threads_lib(pthreads pthread_create CMAKE_HAVE_PTHREADS_CREATE)
       _check_threads_lib(pthread  pthread_create CMAKE_HAVE_PTHREAD_CREATE)
       if(CMAKE_SYSTEM_NAME MATCHES "SunOS")