fix mingw install

Makefile.install

@@ -86,8 +86,8 @@ ifeq ($(OSNAME), Darwin)
 	ln -fs $(LIBDYNNAME) $(LIBPREFIX).dylib
 endif
 ifeq ($(OSNAME), WINNT)
-	@-cp $(LIBDLLNAME) $(OPENBLAS_BINARY_DIR)
-	@-cp $(LIBDLLNAME).a $(OPENBLAS_LIBRARY_DIR)
+	@-cp $(LIBDLLNAME) $(DESTDIR)$(OPENBLAS_BINARY_DIR)
+	@-cp $(LIBDLLNAME).a $(DESTDIR)$(OPENBLAS_LIBRARY_DIR)
 endif
 ifeq ($(OSNAME), CYGWIN_NT)
 	@-cp $(LIBDLLNAME) $(OPENBLAS_BINARY_DIR)