build-sys: use non-recursive build

For reasons see excellent paper 'Recursive Make Considered Harmful' by
Peter Miller.

References: http://miller.emu.id.au/pmiller/books/rmch/
Signed-off-by: Sami Kerola <kerolasa@iki.fi>

doc/.gitignore

@@ -1,5 +0,0 @@
-/Makefile
-/Makefile.in
-/doxy.conf
-/doxyfile.stamp
-/html

doc/Makefile.am

@@ -1,18 +0,0 @@
-EXTRA_DIST = doxy.conf.in introduction.dox
-
-if ENABLE_DOXYGEN
-
-doxyfile.stamp:
-	$(DOXYGEN) doxy.conf
-	date > doxyfile.stamp
-
-CLEANFILES = doxyfile.stamp
-
-all-local: doxyfile.stamp
-
-clean-local: clean-local-check
-.PHONY: clean-local-check
-clean-local-check:
-	-rm -rf html
-
-endif

doc/Makemodule.am

@@ -0,0 +1,20 @@
+EXTRA_DIST += \
+	doc/doxy.conf.in \
+	doc/introduction.dox
+
+if ENABLE_DOXYGEN
+
+doxyfile.stamp:
+	$(DOXYGEN) doc/doxy.conf
+	date > doc/doxyfile.stamp
+
+CLEANFILES += doc/doxyfile.stamp
+
+all-local: doc/doxyfile.stamp
+
+clean-local-doc:
+	-rm -rf doc/*html
+
+CLEAN_LOCALS += clean-local-doc
+
+endif