re PR target/18444 (Multithreading broken on Unix95-class platforms)

	PR target/18444
	* configure.ac (threading): Accept 'posix95'.
	* configure: Regenerate.
	* config.gcc (i[34567]86-*-solaris2*): On Solaris up to 2.6,
	include sol26.h and default to posix95 threads if have_pthread_h.
	(sparc-*-solaris2*): Likewise.
	* gthr.h: Include gthr-posix95.h if _PTHREADS95 is defined.
	* gthr-posix95.h: New file.
	* config/sol26.h: New file.
	* doc/install.texi (--enable-threads): Document 'posix95'.

From-SVN: r91041