[libstdc++] Use LD_RUN_PATH when linking abi_check

[Benjamin Kosnik]

> > Indeed: the current config/linker-map.gnu is GNU ld specific in two ways:
> 
> Yes.  That's the point.  That's the ".gnu" in the name of the file.  :-)

Yep. I'm assuming the Solaris version would be config/linker-map.sun or
whatever.

> There are some 3000 exported symbols.  I flat refuse to track a master
> copy of those by hand in any form, especially mangled.

Couldn't the info in the baseline files be imported for this....

> I have no problem with a generated config/linker-map.sun (or whatever) file.
> But replacing linker-map.gnu with a dummified expanded version is right out.

Yep.

-benjamin