[build] Darwin build of Android port (#3520)

Makefile

@@ -312,9 +312,9 @@ androidupdate: all
 	cp $(INSTALL_DIR)/koreader/git-rev $(INSTALL_DIR)/koreader/ota-rev
 	# don't update the git-rev so that the next start won't revert back
 	# the older 7z version in the assets
-	sed -i '/git-rev/d' $(INSTALL_DIR)/koreader/ota/package.index
+	$(ISED) '/git-rev/d' $(INSTALL_DIR)/koreader/ota/package.index
 	# make gzip android update for zsync OTA update
-	cd $(INSTALL_DIR)/koreader && \
+	-cd $(INSTALL_DIR)/koreader && \
 		tar czafh ../../koreader-android-$(MACHINE)-$(VERSION).targz \
 		-T ota/package.index --no-recursion
 	# make android update apk

README.md

@@ -101,7 +101,8 @@ ld: cannot find -lglib-2.0`
 
 Mac OSX users may need to install these tools:
 ```
-brew install nasm binutils libtool autoconf automake cmake makedepend sdl2 lua51
+brew install nasm binutils libtool autoconf automake cmake makedepend sdl2 lua51 gettext
+echo 'export PATH="/usr/local/opt/gettext/bin:$PATH"' >> ~/.bash_profile
 ```
 
 The KOReader Android build requires `ant`, `openjdk-8-jdk` and `p7zip-full`. A compatible version of the Android NDK and SDK will be downloaded automatically by `./kodev build android` if no NDK or SDK is provided in environment variables. For that purpose you can use `NDK=/ndk/location SDK=/sdk/location ./kodev build android`.