refs #4668: Fix inconsistency of rmdir w.r.t. mkdir/chdir (#4669)

Especially, prefer `_rmdir` on MinGW.

Co-authored-by: Thomas Beutlich <beutlich@users.noreply.github.com>

Author: beutlich

Modelica/Resources/C-Sources/ModelicaInternal.c

@@ -384,10 +384,12 @@ void ModelicaInternal_mkdir(_In_z_ const char* directoryName) {
 
 void ModelicaInternal_rmdir(_In_z_ const char* directoryName) {
     /* Remove directory */
-#if defined(__WATCOMC__) || defined(__LCC__) || defined(_POSIX_) || defined(__GNUC__)
+#if defined(__WATCOMC__) || defined(__LCC__)
     int result = rmdir(directoryName);
 #elif defined(__BORLANDC__) || defined(_WIN32)
     int result = _rmdir(directoryName);
+#elif defined(_POSIX_) || defined(__GNUC__)
+    int result = rmdir(directoryName);
 #else
     ModelicaNotExistError("ModelicaInternal_rmdir");
 #endif