Don't use pthread when on MinGW even if available

It's not supported, and native Windows threading is available for MinGW

googletest/cmake/internal_utils.cmake

@@ -46,7 +46,9 @@ endmacro()
 # Google Mock.  You can tweak these definitions to suit your need.  A
 # variable's value is empty before it's explicitly assigned to.
 macro(config_compiler_and_linker)
-  if (NOT gtest_disable_pthreads)
+  # Note: pthreads on MinGW is not supported, even if available
+  # instead, we use windows threading primitives
+  if (NOT gtest_disable_pthreads AND NOT MINGW)
     # Defines CMAKE_USE_PTHREADS_INIT and CMAKE_THREAD_LIBS_INIT.
     find_package(Threads)
   endif()