[doc] fix broken anchor in install.texi

[Gerald Pfeifer]

On Sun, 13 Nov 2011, Jonathan Wakely wrote:
>> Jonathan, I am a bit confused because if I use the online documentation
>> at http://gcc.gnu.org/install/specific.html the anchor is already of the
>> form "sparc-sun-solaris210", that is, without the dot, and it works just
>> fine.
> The list of targets at the top of the page includes
> x86_64-*-solaris2.1[0-9]* which is a hyperlink to
> http://gcc.gnu.org/install/specific.html#x86-64-x-solaris210

Ah, my bad.  Somehow my brain automatically reads sparc when seeing
solaris. :-)

> Does clicking x86_64-*-solaris2.1[0-9]* work for you?

It does not, and your patch should fix that, indeed.  Thanks!

Gerald