Support GPU emulation standalone build.

This patch modifies the emulator's standalone build system
to rebuild all GPU emulation libraries directly from sources,
assuming their are located under ../../sdk/emulator/opengl/
or ../opengl/

Change-Id: I2ac8fc4bc2d06561dc52298689840f74171397aa
diff --git a/Android.mk b/Android.mk
index 0b02fdb..de7b9d4 100644
--- a/Android.mk
+++ b/Android.mk
@@ -2,9 +2,5 @@
 # through the 'm' or 'mm' build commands. if not, we use the
 # standard QEMU Makefile
 #
-ifeq ($(DEFAULT_GOAL),droid)
-    LOCAL_PATH:= $(call my-dir)
-    include $(LOCAL_PATH)/Makefile.android
-else
-    include Makefile.qemu
-endif
+LOCAL_PATH:= $(call my-dir)
+include $(LOCAL_PATH)/Makefile.android