(alpha-*-linux-gnu*): Default thread_file is `posix'.

From-SVN: r14375

gcc/configure.in

@@ -265,6 +265,9 @@ for machine in $build $host $target; do
 		fixincludes=Makefile.in
 		extra_parts="crtbegin.o crtbeginS.o crtend.o crtendS.o"
 		gas=yes gnu_ld=yes
+ 		if [[ x$thread_file = x ]]; then
+ 			thread_file='posix'
+ 		fi
 		;;
 	alpha-dec-osf[[456789]]*)
 		if [[ x$stabs = xyes ]]