Update 64bit tests to also use EMULATOR_BUILD_64BITS.

Following 18c664d these tests fail to compile on mac since they link to
a library that's not being built any more. Looks like these conditionals
were missed when introducing the define in af061c5.

Change-Id: I5c7ae3eefb31bbef43742c9f17f01ecf1270bb29
diff --git a/Makefile.tests b/Makefile.tests
index d97812f..6de9bb0 100644
--- a/Makefile.tests
+++ b/Makefile.tests
@@ -37,7 +37,7 @@
 $(call end-emulator-program)
 
 
-ifneq ($(filter linux darwin,$(HOST_OS)),)
+ifdef EMULATOR_BUILD_64BITS
   $(call start-emulator-program, emulator64_unittests)
   LOCAL_C_INCLUDES += $(EMULATOR_GTEST_INCLUDES)
   LOCAL_LDLIBS += $(EMULATOR_GTEST_LDLIBS)
diff --git a/distrib/googletest/Android.mk b/distrib/googletest/Android.mk
index 151a3b3..1d0f7b6 100644
--- a/distrib/googletest/Android.mk
+++ b/distrib/googletest/Android.mk
@@ -30,7 +30,7 @@
 LOCAL_SRC_FILES := $(EMULATOR_GTEST_SOURCES)
 $(call end-emulator-library)
 
-ifneq ($(filter linux darwin,$(HOST_OS)),)
+ifdef EMULATOR_BUILD_64BITS
     $(call start-emulator-library, emulator64-libgtest)
     LOCAL_C_INCLUDES += $(EMULATOR_GTEST_INCLUDES)
     LOCAL_CPP_EXTENSION := .cc