[PATCH] Turn ___brk_addr into a compat symbol

[Florian Weimer]

* Andreas Schwab:

> GCC hasn't been requiring the ___brk_addr symbol since 3.1, and before
> that only on i386 at least since 2.95.

GCC 2.7.2.3 uses it as well on i386.

I think turning it into a compatibility symbol will prevent users from
using these compilers to link new binaries.