Tie in the doc build flags with the top level Makefile.

Makefile.in

@@ -7,8 +7,12 @@ DAT_DIR = share
 SRC_DIR = src
 
 HAVE_PYTHON = @HAVE_PYTHON@
+
 HAVE_DOCKER = @HAVE_DOCKER@
 
+CAN_BUILD_CXX_DOCS = @HAVE_CXX_DOCS@
+CAN_BUILD_PYTHON_DOCS = @HAVE_PYTHON_DOCS@
+
 BIFROST_PYTHON_DIR = python
 
 all: libbifrost python
@@ -63,8 +67,13 @@ ifeq ($(HAVE_PYTHON),1)
 endif
 .PHONY: uninstall
 
-doc: $(INC_DIR)/bifrost/*.h Doxyfile
+doc: $(INC_DIR)/bifrost/*.h Doxyfile docs/source/*.rst docs/source/*.py
+ifeq ($(CAN_BUILD_CXX_DOCS),1)
 	@DX_DOXYGEN@ Doxyfile
+endif
+ifeq ($(CAN_BUILD_PYTHON_DOCS),1)
+	$(MAKE) -C docs singlehtml
+endif
 .PHONY: doc
 
 python: libbifrost