default_settings: adding mcf threading model to GCC on Windows

Since the introduction of the mingw-builds/13.2.0 with
conan-io/conan-center-index#23481 PR, GCC now
support an additional threading model which is called mcf. But this
settings is missing from the default configuration

conan/internal/default_settings.py

@@ -113,7 +113,7 @@
                     "13", "13.1", "13.2", "13.3",
                     "14", "14.1", "14.2"]
         libcxx: [libstdc++, libstdc++11]
-        threads: [null, posix, win32]  # Windows MinGW
+        threads: [null, posix, win32, mcf]  # Windows MinGW
         exception: [null, dwarf2, sjlj, seh]  # Windows MinGW
         cppstd: [null, 98, gnu98, 11, gnu11, 14, gnu14, 17, gnu17, 20, gnu20, 23, gnu23, 26, gnu26]
         cstd: [null, 99, gnu99, 11, gnu11, 17, gnu17, 23, gnu23]