Double the size of ARG_MAX on LP64 platforms.

As modern software keeps growing in size, we get requests to update the
value of ARG_MAX in order to link the resulting object files. Other OSs
have much higher values but Increasiong ARG_MAX has a multiplied effect on
KVA, so just bumping this value is dangerous in some archs like ARM32 that
can exhaust KVA rather easily.

While it would be better to have a unique value for all archs, other OSs
(Illumos in partidular) can have different ARG_MAX limits depending on the
platform, For now we want to be really conservative so we are avoidng
the change on ILP32 and in the alternative case we only double it since that
seems to work well enough for recent Code Aster.

I was planning to bump the _FreeBSD_version but it was bumped recently
(r355798) so we can reuse the 1300068 value for this change.

PR: 241710
MFC after: 5 days