RFA: PR gold/27815 fix may require GCC newer than current minimum version

[Fangrui Song]

On 2021-05-05, Cary Coutant via Binutils wrote:
>PR gold/27815 reports a new build failure where we use a deprecated
>std::pair constructor using NULL. As far as I can tell, the proper fix
>is to use nullptr instead of NULL, but nullptr is only supported in
>GCC 4.6 and later. Gold currently claims to be buildable with GCC
>4.1.3.
>
>Does anyone care if I raise the minimum version of GCC for building
>gold to 4.6 (or maybe later)? I certainly wouldn't mind the freedom to
>use some newer C++ features.
>
>-cary

Bumping to GCC>=4.6 looks good.