* configure.in: check if succeeded in creating config.h.

	* tool/ifchange: ignore failures when TEST_COLORS unmatched. just
	  use the default value if expected name is not contained in it.
	  [ruby-core:75046] [Bug #12303]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@54710 b2dd03c8-39d4-4d8f-98ff-823fe69b080e