test: force legacy mangling for run-make-fulldeps/a-b-a-linker-guard.

Author: eddyb

src/test/run-make-fulldeps/a-b-a-linker-guard/Makefile

@@ -4,9 +4,12 @@
 # of types, it will not run with a dylib that has a different set of
 # types.
 
+# NOTE(eddyb) this test only works with the `legacy` mangling,
+# and will probably get removed once `legacy` is gone.
+
 all:
-	$(RUSTC) a.rs --cfg x -C prefer-dynamic
-	$(RUSTC) b.rs -C prefer-dynamic
+	$(RUSTC) a.rs --cfg x -C prefer-dynamic -Z symbol-mangling-version=legacy
+	$(RUSTC) b.rs -C prefer-dynamic -Z symbol-mangling-version=legacy
 	$(call RUN,b)
-	$(RUSTC) a.rs --cfg y -C prefer-dynamic
+	$(RUSTC) a.rs --cfg y -C prefer-dynamic -Z symbol-mangling-version=legacy
 	$(call FAIL,b)