Work around the fact that Linux and Mac OS have opposite requirements for libgtest.

This should let us keep the working Mac build without breaking the Linux build!

Change-Id: I2ec44b7043c8ac9be49f0068d9eb7e18e9c88c7d
diff --git a/build/Android.common.mk b/build/Android.common.mk
index 7c53206..a404231 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -72,7 +72,7 @@
 
 ifneq ($(HOST_OS),linux)
   # Some Mac OS pthread header files are broken with -fkeep-inline-functions.
-  ART_HOST_DEBUG_CFLAGS := $(filter-out -fkeep-inline-functions,)
+  ART_HOST_DEBUG_CFLAGS := $(filter-out -fkeep-inline-functions,$(ART_HOST_DEBUG_CFLAGS))
 endif
 
 ART_TARGET_DEBUG_CFLAGS := $(art_debug_cflags)