[Docs] Fix Sphinx incremental build. Patch by Sean Silva!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163235 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/Makefile.sphinx b/docs/Makefile.sphinx
index 21f6648..81c13de 100644
--- a/docs/Makefile.sphinx
+++ b/docs/Makefile.sphinx
@@ -46,6 +46,10 @@
 html:
 	$(SPHINXBUILD) -b html $(ALLSPHINXOPTS) $(BUILDDIR)/html
 	@echo
+	@# FIXME: Remove this `cp` once HTML->Sphinx transition is completed.
+	@# Kind of a hack, but HTML-formatted docs are on the way out anyway.
+	@echo "Copying legacy HTML-formatted docs into $(BUILDDIR)/html"
+	@cp -a *.html tutorial $(BUILDDIR)/html
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."
 
 dirhtml: