I also noticed that even if _rmdir is available in MinGW header direct.h, ModelicaInternal.c uses rmdir in line 388 and not _rmdir of line 390. Hence, it is not consistent between _mkdir/_chdir and _rmdir.

ModelicaStandardLibrary/Modelica/Resources/C-Sources/ModelicaInternal.c

Lines 385 to 393 in c2dabe7

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

Originally posted by @beutlich in #4664