Re-enable TLS on x86_64 when cross-building.

Building gcc on x86_64 with TLS enabled has been fixed,
so this is to keep cross-builds and native builds in
sync.

build/scripts/build_cross_tools_gcc4

@@ -25,10 +25,6 @@ x86_64-*)
 	# explicitly using --enable-multilib that causes a build
 	# failure
 	binutilsConfigureArgs=""
-	# 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-*)