Add a test that rustc compiles and links separately

Victor Ding · Victor Ding · commit e8a564edc0a0 · 2020-12-23T12:51:10.000+11:00
diff --git a/src/test/run-make-fulldeps/separate-link/Makefile b/src/test/run-make-fulldeps/separate-link/Makefile
@@ -0,0 +1,6 @@
+-include ../tools.mk
+
+all:
+	echo 'fn main(){}' | $(RUSTC) -Z no-link -
+	$(RUSTC) -Z link-only $(TMPDIR)/rust_out.rlink
+	$(call RUN,rust_out)
