Add script to build many glibc configurations

[Joseph Myers]

On Thu, 10 Nov 2016, Steve Ellcey wrote:

> Joseph, it appears that when building the cross compilers, there is no
> way to restrict that to just the compilers for certain targets. Â Is
> that correct? Â On one hand I can understand that, since that gives you

You can specify arguments <dir> compilers target1 target2 ...

(where the targets are ARCH-linux-gnu or ARCH-linux-gnu-variant for one of 
the variants listed in the script).  Then for the glibc step specify 
similar arguments (note that ARCH and variant names may be different for 
the glibcs in cases where a compiler has more than one glibc).

-- 
Joseph S. Myers
joseph@codesourcery.com