Add support for TARGET_GLOBAL_UNSUPPORTED_CFLAGS

To ease the transition between toolchains, allow a target to specify
a list of cflags that the toolchain does not support.  These will be
filtered out of the cflags provided by the module.

Add TARGET_GLOBAL_UNSUPPORTED_CFLAGS := -fstack-protector for the
aarch64 toolchain, it does not yet suport -fstack-protector.

Change-Id: I168d0c6f131326fad305ec86fad46e6a3e03295a
diff --git a/core/combo/TARGET_linux-arm64.mk b/core/combo/TARGET_linux-arm64.mk
index a175eab..76ee567 100644
--- a/core/combo/TARGET_linux-arm64.mk
+++ b/core/combo/TARGET_linux-arm64.mk
@@ -91,6 +91,9 @@
 			-include $(android_config_h) \
 			-I $(dir $(android_config_h))
 
+# HACK: globally disable -fstack-protector until the toolchain supports it
+TARGET_GLOBAL_UNSUPPORTED_CFLAGS := -fstack-protector
+
 # TODO - remove __ANDROID__ after the next aarch64 toolchain refresh
 TARGET_GLOBAL_CFLAGS += -D__ANDROID__=1