Fix emulator standalone build

Fix Makefile.android to build emulator if at least one of
BUILD_EMULATOR and BUILD_STANDALONE_EMULATOR is true

Change-Id: I55be207a78e0e96047b6cfcd45feebeff03c2c57
diff --git a/Makefile.android b/Makefile.android
index 181986a..c7d43af 100644
--- a/Makefile.android
+++ b/Makefile.android
@@ -1,4 +1,4 @@
-ifeq ($(BUILD_EMULATOR),true)
+ifneq ($(filter true% %true,$(BUILD_EMULATOR)$(BUILD_STANDALONE_EMULATOR)),)
 
 ifneq (,$(filter $(TARGET_ARCH),arm x86 mips))
 LOCAL_PATH:= $(call my-dir)
@@ -309,4 +309,4 @@
 ## VOILA!!
 
 endif  # TARGET_ARCH == arm || TARGET_ARCH == x86 || TARGET_ARCH == mips
-endif  # BUILD_EMULATOR
+endif  # BUILD_EMULATOR == true || BUILD_STANDALONE_EMULATOR == true