Replace rustdoc-ui/{c,z}-help tests with a run-make test

This make rustdoc resilient to changes in the debugging options while
still testing that it matches rustc.

Author: jyn514

tests/run-make/rustdoc-shared-flags/Makefile

@@ -0,0 +1,18 @@
+include ../tools.mk
+
+all: z_help c_help list_passes
+
+c_help:
+	$(RUSTC) -C help > $(TMPDIR)/rustc.c_help.txt
+	$(RUSTDOC) -C help > $(TMPDIR)/rustdoc.c_help.txt
+	$(DIFF) $(TMPDIR)/rustc.c_help.txt $(TMPDIR)/rustdoc.c_help.txt
+
+z_help:
+	$(RUSTC) -Z help > $(TMPDIR)/rustc.z_help.txt
+	$(RUSTDOC) -Z help > $(TMPDIR)/rustdoc.z_help.txt
+	$(DIFF) $(TMPDIR)/rustc.z_help.txt $(TMPDIR)/rustdoc.z_help.txt
+
+list_passes:
+	$(RUSTC) -C passes=list > $(TMPDIR)/rustc.passes.txt
+	$(RUSTDOC) -C passes=list > $(TMPDIR)/rustdoc.passes.txt
+	$(DIFF) $(TMPDIR)/rustc.passes.txt $(TMPDIR)/rustdoc.passes.txt