Patch RFA: Support for building Go tools

[Ian Lance Taylor]

Committed initial gotools patch with following ChangeLog entries:

./:

2015-01-09  Ian Lance Taylor  <iant@google.com>

	* configure.ac (host_tools): Add gotools.
	* Makefile.def (host_modules): Add gotools.
	(dependencies): Add dependency of all-gotools on all-target-libgo.

gcc/go/:

2015-01-09  Ian Lance Taylor  <iant@google.com>

	* config-lang.in (lang_dirs): Define.

gotools/:

2015-01-09  Ian Lance Taylor  <iant@google.com>

	* Initial implementation.