Makefile: Fix missing slashes (GH-28659)

Author: native-api

Makefile.pre.in

@@ -1443,13 +1443,13 @@ altbininstall: $(BUILDPYTHON) @FRAMEWORKPYTHONW@
 		fi; \
 	fi
 	if test "x$(LIPO_32BIT_FLAGS)" != "x" ; then \
-		rm -f $(DESTDIR)$(BINDIR)python$(VERSION)-32$(EXE); \
+		rm -f $(DESTDIR)$(BINDIR)/python$(VERSION)-32$(EXE); \
 		lipo $(LIPO_32BIT_FLAGS) \
 			-output $(DESTDIR)$(BINDIR)/python$(VERSION)-32$(EXE) \
 			$(DESTDIR)$(BINDIR)/python$(VERSION)$(EXE); \
 	fi
 	if test "x$(LIPO_INTEL64_FLAGS)" != "x" ; then \
-		rm -f $(DESTDIR)$(BINDIR)python$(VERSION)-intel64$(EXE); \
+		rm -f $(DESTDIR)$(BINDIR)/python$(VERSION)-intel64$(EXE); \
 		lipo $(LIPO_INTEL64_FLAGS) \
 			-output $(DESTDIR)$(BINDIR)/python$(VERSION)-intel64$(EXE) \
 			$(DESTDIR)$(BINDIR)/python$(VERSION)$(EXE); \

Misc/NEWS.d/next/Build/2021-10-01-12-20-05.bpo-0.2ykYK2.rst

@@ -0,0 +1 @@
+Makefile: fix missing slashes in some invocations cleaning previous build results when builing a macOS universal binary.