Add a test that -Zquery-dep-graph -Zdump-dep-graph works

Author: Mark-Simulacrum

src/test/run-make/dep-graph/Makefile

@@ -0,0 +1,10 @@
+-include ../../run-make-fulldeps/tools.mk
+
+# Just verify that we successfully run and produce dep graphs when requested.
+
+all:
+	RUST_DEP_GRAPH=$(TMPDIR)/dep-graph $(RUSTC) \
+        -Cincremental=$(TMPDIR)/incr \
+        -Zquery-dep-graph -Zdump-dep-graph foo.rs
+	test -f $(TMPDIR)/dep-graph.txt
+	test -f $(TMPDIR)/dep-graph.dot

src/test/run-make/dep-graph/foo.rs

@@ -0,0 +1 @@
+fn main() {}