Fix android_arm build hosted on Mac

Makefile.android

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 17 matching lines @@
 # Those definitions should be consistent with the main Makefile
 ANDROID_ARCHES = android_ia32 android_x64 android_arm android_arm64 \
                  android_mipsel android_x87
 MODES = release debug
 
 # Generates all combinations of ANDROID ARCHES and MODES,
 # e.g. "android_ia32.release" or "android_arm.release"
 ANDROID_BUILDS = $(foreach mode,$(MODES), \
                    $(addsuffix .$(mode),$(ANDROID_ARCHES)))
 
+HOST_OS = $(shell uname -s | sed -e 's/Linux/linux/;s/Darwin/darwin/')
+HOST_ARCH = $(shell uname -m | sed -e 's/i[3456]86/x86/')
+
 ifeq ($(ARCH), android_arm)
   DEFINES  = target_arch=arm v8_target_arch=arm
+  ANDROID_TOOLCHAIN = $(ANDROID_NDK_ROOT)/toolchains/arm-linux-androideabi-4.9/prebuilt/$(HOST_OS)-$(HOST_ARCH)/arm-linux-androideabi/bin
 else ifeq ($(ARCH), android_arm64)
   DEFINES  = target_arch=arm64 v8_target_arch=arm64
+  ANDROID_TOOLCHAIN = $(ANDROID_NDK_ROOT)/toolchains/aarch64-linux-android-4.9/prebuilt/$(HOST_OS)-$(HOST_ARCH)/aarch64-linux-android/bin
 else ifeq ($(ARCH), android_mipsel)
   DEFINES  = target_arch=mipsel v8_target_arch=mipsel
+  ANDROID_TOOLCHAIN = $(ANDROID_NDK_ROOT)/toolchains/mipsel-linux-android-4.9/prebuilt/$(HOST_OS)-$(HOST_ARCH)/mipsel-linux-android/bin
 else ifeq ($(ARCH), android_ia32)
   DEFINES = target_arch=ia32 v8_target_arch=ia32
+  ANDROID_TOOLCHAIN = $(ANDROID_NDK_ROOT)/toolchains/x86-4.9/prebuilt/$(HOST_OS)-$(HOST_ARCH)/i686-linux-android/bin
 else ifeq ($(ARCH), android_x64)
   DEFINES = target_arch=x64 v8_target_arch=x64
+  ANDROID_TOOLCHAIN = $(ANDROID_NDK_ROOT)/toolchains/x86_64-4.9/prebuilt/$(HOST_OS)-$(HOST_ARCH)/x86_64-linux-android/bin
 else ifeq ($(ARCH), android_x87)
   DEFINES = target_arch=ia32 v8_target_arch=x87
+  ANDROID_TOOLCHAIN = $(ANDROID_NDK_ROOT)/toolchains/x86-4.9/prebuilt/$(HOST_OS)-$(HOST_ARCH)/i686-linux-android/bin
 else
   $(error Target architecture "${ARCH}" is not supported)
 endif
 
 # Common flags.
 DEFINES += OS=android
 
 .SECONDEXPANSION:
 $(ANDROID_BUILDS): $(OUTDIR)/Makefile.$$@
         @$(MAKE) -C "$(OUTDIR)" -f Makefile.$@ \
+                  AR="$(ANDROID_TOOLCHAIN)/ar" \
                   BUILDTYPE=$(shell echo $(subst .,,$(suffix $@)) | \
                               python -c "print raw_input().capitalize()") \
                   builddir="$(shell pwd)/$(OUTDIR)/$@"
 
 # Android GYP file generation targets.
 ANDROID_MAKEFILES = $(addprefix $(OUTDIR)/Makefile.,$(ANDROID_BUILDS))
 $(ANDROID_MAKEFILES):
         GYP_GENERATORS=make-android \
         GYP_DEFINES="${DEFINES}" \
         PYTHONPATH="$(shell pwd)/tools/generate_shim_headers:$(shell pwd)/build:$(PYTHONPATH)" \
         build/gyp/gyp --generator-output="${OUTDIR}" build/all.gyp \
                       -Ibuild/standalone.gypi --depth=. \
                       -S$(suffix $(basename $@))$(suffix $@) ${GYPFLAGS}