PATCH RFC: Recognize gold in libstdc++ configure script

[Benjamin Kosnik]

> Most of the linker configure tests (e.g., config.guess, libtool) look
> at the --help output.  Of course libstdc++ has a good reason for
> checking the version number.  The gcc configure script also checks the
> version number, but it happens to work correctly for gold through what
> is essentially a lucky accident.
> 
> So I guess my general plan is to find cases which check the version
> number.  Where possible I want to change them to check something else,
> and where not possible I want to change them to check for gold.

Great. This is what I was looking for.

Checking --help output is a method that seems to work well for
both ld and gold, and what libstdc++ config should strive to use in the
future. 

Too bad we can't do the --gc-sections check this way.

-benjamin