Disable 64-bit Darwin platform build.

Apparently, this builds fails when using a more recent version
of XCode due to conflicts with libcompiler_rt.dylib. Temporarily
disable these until the relevant issue is fixed.

Does not affect standalone builds.

Change-Id: Ie84ec4f3474fd7c97181bee897e6e9ea0fb864e0
diff --git a/Makefile.android b/Makefile.android
index 739143a..b5a6008 100644
--- a/Makefile.android
+++ b/Makefile.android
@@ -255,6 +255,13 @@
 # yet due to differing procedure call ABI conventions.
 EMULATOR_BUILD_64BITS := $(strip $(filter linux darwin,$(HOST_OS)))
 
+# Disable 64-bit build for Darwin platform builds.
+ifeq ($(HOST_OS),darwin)
+ifneq (true,$(BUILD_STANDALONE_EMULATOR))
+EMULATOR_BUILD_64BITS := $(strip $(empty))
+endif # BUILD_STANDALONE_EMULATOR != true
+endif # HOST_OS == darwin
+
 include $(LOCAL_PATH)/Makefile.common
 
 ifeq ($(HOST_OS),windows)