fix: add /usr/local/lib64 to LD search path

[mwtoews]

This (untested) fix adds /usr/local/lib64 to manylinux images (except i686, which doesn't have this dir).

Fixes #1886

[mayeut]

Thanks for the contribution,
Given it's untested here and commented as such, does this actually fix #1886 (i.e. tested downstream) ?

[mwtoews]

I have since enabled this downstream in shapely/shapely@414315c which works as expected.

I can't think of anything simple to add to docker/tests. The best "simple" would be to build and install some exampled shared library then test to see if it install and correctly links to a shared library in /usr/local/lib64.