Support an ad-hoc (non-gbuild) Makefile workflow for the Android apps

For now, we want to keep being able to just say for instance "make run" in the
android app directories.

Change-Id: I1898d5466c0df6007fa32b202888bed644fa9489

android/experimental/DocumentLoader/Makefile

-include $(BUILDDIR)/config_host.mk
+ifeq ($(BUILDDIR),)
+include ../../../config_host.mk
+endif
 
 # The default target just builds.
 all: build-ant

android/experimental/LibreOffice4Android/Makefile

-include $(BUILDDIR)/config_host.mk
+ifeq ($(BUILDDIR),)
+include ../../../config_host.mk
+endif
 
 # The default target just builds.
 

android/experimental/desktop/Makefile

-include $(BUILDDIR)/config_host.mk
+ifeq ($(BUILDDIR),)
+include ../../../config_host.mk
+endif
 
 # The default target just builds.
 all: build-ant

android/sdremote/Makefile

@@ -6,7 +6,9 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-include $(BUILDDIR)/config_host.mk
+ifeq ($(BUILDDIR),)
+include ../../config_host.mk
+endif
 
 all: properties translations.done
 	mkdir -p ../abs-lib/libs