* config.gcc: Stop changing enable_threads midstream.

	Replace uses of enable_threads_flag with enable_threads.
	* configure.ac: Replace uses of enable_threads_flag with
	enable_threads.  Improve autoconf quotation in one place.
	* configure: Regenerate.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@80473 138bc75d-0d04-0410-961f-82ee72b054a4