Ensure that building of tests/libtest.so respects our LDFLAGS.

diff -upr a/Makefile b/Makefile
--- a/Makefile	2026-07-06 21:05:39.442671225 +0200
+++ b/Makefile	2026-07-06 21:07:01.478498796 +0200
@@ -123,7 +123,7 @@ libpatch.so: $(OBJECTS)
 	$(QUIET_LINK) $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) -shared -o $@ $^ $(LIBS)
 
 tests/libtest.so: $(TOBJECTS)
-	$(QUIET_LINK) $(CC) -shared -o $@ $^
+	$(QUIET_LINK) $(CC) $(LDFLAGS) -shared -o $@ $^
 
 %.o: %.c
 	$(QUIET_CC) $(CC) $(CPPFLAGS) -MMD $(CFLAGS) -fPIC -c -o $@ $<