Disable TLS support on x86_64 explicitly.

* Building gcc-4.8.3 on x86_64 with TLS support fails with an internal
  compiler error. Until that problem is fixed, don't use TLS on x86_64,
  which (due to libstdc++ compatibility) requires the same for the
  host cross compiler.

build/scripts/build_cross_tools_gcc4

@@ -25,7 +25,10 @@ x86_64-*)
 	# explicitly using --enable-multilib that causes a build
 	# failure
 	binutilsConfigureArgs=""
-	gccConfigureArgs=""
+	# TODO: trying to build gcc-4.8.3 on x86_64 with --enable-tls fails with an
+	# internal compiler error, so we disable it (overriding --enable-tls used
+	# in the configure invocation below) until that problem is solved.
+	gccConfigureArgs="--disable-tls"
 	kernelCcFlags="$kernelCcFlags -mno-red-zone"
 	;;
 m68k-*)