Add test

src/test/run-make-fulldeps/hotplug_codegen_backend/Makefile

@@ -2,10 +2,25 @@ include ../tools.mk
 
 # ignore-stage1
 
+# This test both exists as a check that -Zcodegen-backend is capable of loading external codegen
+# backends and that this external codegen backend is only included in the dep info if
+# -Zbinary-dep-depinfo is used.
+
 all:
 	/bin/echo || exit 0 # This test requires /bin/echo to exist
 	$(RUSTC) the_backend.rs --crate-name the_backend --crate-type dylib \
 		-o $(TMPDIR)/the_backend.dylib
+
+	$(RUSTC) some_crate.rs --crate-name some_crate --crate-type lib -o $(TMPDIR)/some_crate \
+		-Z codegen-backend=$(TMPDIR)/the_backend.dylib -Z unstable-options \
+		--emit link,dep-info
+	grep -x "This has been \"compiled\" successfully." $(TMPDIR)/libsome_crate.rlib
+	# don't declare a dependency on the codegen backend if -Zbinary-dep-depinfo isn't used.
+	grep -v "the_backend.dylib" $(TMPDIR)/some_crate.d
+
 	$(RUSTC) some_crate.rs --crate-name some_crate --crate-type lib -o $(TMPDIR)/some_crate \
-		-Z codegen-backend=$(TMPDIR)/the_backend.dylib -Z unstable-options
-	grep -x "This has been \"compiled\" successfully." $(TMPDIR)/some_crate
+		-Z codegen-backend=$(TMPDIR)/the_backend.dylib -Z unstable-options \
+		--emit link,dep-info -Zbinary-dep-depinfo
+	grep -x "This has been \"compiled\" successfully." $(TMPDIR)/libsome_crate.rlib
+	# but declare a dependency on the codegen backend if -Zbinary-dep-depinfo it used.
+	grep "the_backend.dylib" $(TMPDIR)/some_crate.d