support --with-multilib-list=@name for ARM

support --with-multilib-list=@name for ARM

Introduce @name as a means to specify alternate multilib profiles as
arguments to --with-multilib-list.

So far this is only implemented for ARM.

for  gcc/ChangeLog

	* config.gcc (tmake_file): Add name to tmake_file for
        each @name in --with-multilib-list on arm-*-* targets.
	* doc/install.texi (with-multilib-list): Document it.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@267320 138bc75d-0d04-0410-961f-82ee72b054a4