Use aarch64-linux-android-4.9 for arm64 build (attempt #3)

GCC: 4.9 (which supports -fstack-protector)
Binutils: 2.24 (which supports gc-sections)
GDB: 7.7

NDK libraries are still picked up from prebuilts/ndk/*/4.8/*
GCC has been patched to disable codegen for calling
__cxa_throw_bad_array_new_length.

Change-Id: Ie0bf38357c0cf3d265d8b5dd3c2b8a8fd83b1de1

core/combo/TARGET_linux-arm64.mk

@@ -38,7 +38,7 @@ endif
 TARGET_NDK_GCC_VERSION := 4.8
 
 ifeq ($(strip $(TARGET_GCC_VERSION_EXP)),)
-TARGET_GCC_VERSION := 4.8
+TARGET_GCC_VERSION := 4.9
 else
 TARGET_GCC_VERSION := $(TARGET_GCC_VERSION_EXP)
 endif
@@ -73,13 +73,9 @@ TARGET_GLOBAL_CFLAGS += \
 
 android_config_h := $(call select-android-config-h,linux-arm64)
 
-# HACK: globally disable -fstack-protector until the toolchain supports it
-TARGET_GLOBAL_UNSUPPORTED_CFLAGS := \
-    -fstack-protector \
-    -fstack-protector-all \
-
 TARGET_GLOBAL_CFLAGS += \
 			-fpic -fPIE \
+			-fstack-protector \
 			-ffunction-sections \
 			-fdata-sections \
 			-funwind-tables \
@@ -163,6 +159,7 @@ TARGET_CUSTOM_LD_COMMAND := true
 define transform-o-to-shared-lib-inner
 $(hide) $(PRIVATE_CXX) \
 	-nostdlib -Wl,-soname,$(notdir $@) \
+	-Wl,--gc-sections \
 	-Wl,-shared,-Bsymbolic \
 	$(PRIVATE_TARGET_GLOBAL_LD_DIRS) \
 	$(if $(filter true,$(PRIVATE_NO_CRT)),,$(PRIVATE_TARGET_CRTBEGIN_SO_O)) \
@@ -186,6 +183,7 @@ endef
 define transform-o-to-executable-inner
 $(hide) $(PRIVATE_CXX) -nostdlib -Bdynamic -fPIE -pie \
 	-Wl,-dynamic-linker,/system/bin/linker64 \
+	-Wl,--gc-sections \
 	-Wl,-z,nocopyreloc \
 	$(PRIVATE_TARGET_GLOBAL_LD_DIRS) \
 	-Wl,-rpath-link=$(PRIVATE_TARGET_OUT_INTERMEDIATE_LIBRARIES) \
@@ -209,6 +207,7 @@ endef
 
 define transform-o-to-static-executable-inner
 $(hide) $(PRIVATE_CXX) -nostdlib -Bstatic \
+	-Wl,--gc-sections \
 	-o $@ \
 	$(PRIVATE_TARGET_GLOBAL_LD_DIRS) \
 	$(if $(filter true,$(PRIVATE_NO_CRT)),,$(PRIVATE_TARGET_CRTBEGIN_STATIC_O)) \