Description
As a result of nodejs/node#14785 and nodejs/help#784 we have discovered that a backwards incompatible change was made in libstdc++ AIX between gcc 4.8 and gcc 4.9. This means that the requirement for GCC 4.9.3 for Node 8 requires that we raise the minimum gcc/libstdc++ version for that platform. Ideally we should do this before Node 8 goes LTS, or stick with gcc 4.8.4 for 8.x.
AIX is a special case here, because it doesn't come with libstdc++ or gcc by default, so everyone running on the platform needs to install gcc in order to run Node. There are two places to get gcc versions, the AIX Toolbox and Bull Freeware. Currently the AIX toolbox only has GCC 6.3.0 available, and Bull Freeware has 7.2.0, 6.4.0, and 5.5.0 (and older minor versions).
It's worth noting at this point that gcc changed their versioning scheme after 4.9, so 4.10 became 5.0, and 4.11 became 6.0. So the gap between 4.9 and 7.0 is not as large as it seems.
Given that AIX users have to download gcc anyway, and given that they will have to update their gcc levels for this release, I think we should bump to a relatively new version (so they don't have to upgrade again for as long as possible). I'd suggest using 6.3.0, GCC 7 came out this year, so might be too new to move to.