Enable building for android on x86_64 machines.

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_arm android_mipsel
 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/mac/')
+ANDROID_NDK_HOST_ARCH ?= $(shell uname -m | sed -e 's/i[3456]86/x86/')
 ifeq ($(HOST_OS), linux)
-  TOOLCHAIN_DIR = linux-x86
+  TOOLCHAIN_DIR = linux-$(ANDROID_NDK_HOST_ARCH)
 else
   ifeq ($(HOST_OS), mac)
-    TOOLCHAIN_DIR = darwin-x86
+    TOOLCHAIN_DIR = darwin-$(ANDROID_NDK_HOST_ARCH)
   else
     $(error Host platform "${HOST_OS}" is not supported)
   endif
 endif
 
 ifeq ($(ARCH), android_arm)
   DEFINES  = target_arch=arm v8_target_arch=arm android_target_arch=arm
   DEFINES += arm_neon=0 armv7=1
   TOOLCHAIN_ARCH = arm-linux-androideabi-4.6
 else
   ifeq ($(ARCH), android_mipsel)
     DEFINES  = target_arch=mipsel v8_target_arch=mipsel android_target_arch=mips
     DEFINES += mips_arch_variant=mips32r2
     TOOLCHAIN_ARCH = mipsel-linux-android-4.6
   else
     ifeq ($(ARCH), android_ia32)
       DEFINES = target_arch=ia32 v8_target_arch=ia32 android_target_arch=x86
       TOOLCHAIN_ARCH = x86-4.6
     else
       $(error Target architecture "${ARCH}" is not supported)
     endif
   endif
 endif
 
 TOOLCHAIN_PATH = ${ANDROID_NDK_ROOT}/toolchains/${TOOLCHAIN_ARCH}/prebuilt
 ANDROID_TOOLCHAIN ?= ${TOOLCHAIN_PATH}/${TOOLCHAIN_DIR}
 ifeq ($(wildcard $(ANDROID_TOOLCHAIN)),)
-  $(error Cannot find Android toolchain in "${ANDROID_TOOLCHAIN}")
+  $(error Cannot find Android toolchain in "${ANDROID_TOOLCHAIN}".  Please \
+          check that ANDROID_NDK_ROOT and ANDROID_NDK_HOST_ARCH are set    \
+          correctly)
 endif
 
 # For mksnapshot host generation.
 DEFINES += host_os=${HOST_OS}
 
 .SECONDEXPANSION:
 $(ANDROID_BUILDS): $(OUTDIR)/Makefile.$$(basename $$@)
         @$(MAKE) -C "$(OUTDIR)" -f Makefile.$(basename $@) \
                     CXX="$(ANDROID_TOOLCHAIN)/bin/*-g++" \
                     AR="$(ANDROID_TOOLCHAIN)/bin/*-ar" \
                     RANLIB="$(ANDROID_TOOLCHAIN)/bin/*-ranlib" \
                     CC="$(ANDROID_TOOLCHAIN)/bin/*-gcc" \
                     LD="$(ANDROID_TOOLCHAIN)/bin/*-ld" \
                     LINK="$(ANDROID_TOOLCHAIN)/bin/*-g++" \
                     BUILDTYPE=$(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_ARCHES))
 $(ANDROID_MAKEFILES):
         @GYP_GENERATORS=make-android \
         GYP_DEFINES="${DEFINES}" \
         CC="${ANDROID_TOOLCHAIN}/bin/*-gcc" \
         CXX="${ANDROID_TOOLCHAIN}/bin/*-g++" \
         build/gyp/gyp --generator-output="${OUTDIR}" build/all.gyp \
                       -Ibuild/standalone.gypi --depth=. -Ibuild/android.gypi \
                       -S.${ARCH} ${GYPFLAGS}