merge revision(s) r45954: [Backport #8358]

	* configure.in: enable SSE2 on mingw. target='i386-pc-mingw32'.
	  [ruby-core:62095] [Bug #8358]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@46467 b2dd03c8-39d4-4d8f-98ff-823fe69b080e