Strip with $(STRIP), not the build host strip.

diff -Nrup a/xr/Makefile b/xr/Makefile
--- a/xr/Makefile	2013-04-06 16:59:09.000000000 +0200
+++ b/xr/Makefile	2026-10-22 17:22:16.751883955 +0200
@@ -25,7 +25,7 @@ foo:
 install: $(BINDIR)/xr
 $(BINDIR)/xr: $(BIN)
 	cp $(BIN) $(TMPXR)
-	strip $(TMPXR)
+	$(STRIP) $(TMPXR)
 	install $(TMPXR) $(BINDIR)/xr
 	rm -f $(TMPXR)