Switch x86 default compiler to multilib version

Switch from gcc-4.7 32-bit only to gcc-4.7 multilib (32/x32/64) compiler.
Tested x86 image build on Linux and Darwin.

This bionic patch is required:
https://android-review.googlesource.com/#/c/64183

Change-Id: Ifc2c6c5d6a4a1b71a00a87af072bb7f67b1c284d
Signed-off-by: Pavel Chupin <pavel.v.chupin@intel.com>
diff --git a/core/combo/TARGET_linux-x86.mk b/core/combo/TARGET_linux-x86.mk
index 159fbe1..7506787 100644
--- a/core/combo/TARGET_linux-x86.mk
+++ b/core/combo/TARGET_linux-x86.mk
@@ -42,8 +42,8 @@
 
 # You can set TARGET_TOOLS_PREFIX to get gcc from somewhere else
 ifeq ($(strip $(TARGET_TOOLS_PREFIX)),)
-TARGET_TOOLCHAIN_ROOT := prebuilts/gcc/$(HOST_PREBUILT_TAG)/x86/i686-linux-android-$(TARGET_GCC_VERSION)
-TARGET_TOOLS_PREFIX := $(TARGET_TOOLCHAIN_ROOT)/bin/i686-linux-android-
+TARGET_TOOLCHAIN_ROOT := prebuilts/gcc/$(HOST_PREBUILT_TAG)/x86/x86_64-linux-android-$(TARGET_GCC_VERSION)
+TARGET_TOOLS_PREFIX := $(TARGET_TOOLCHAIN_ROOT)/bin/x86_64-linux-android-
 endif
 
 TARGET_CC := $(TARGET_TOOLS_PREFIX)gcc$(HOST_EXECUTABLE_SUFFIX)