Find libgit2 in LD_LIBRARY_PATH

[lukego]

It would be wonderful if Iceberg could find libgit2 in LD_LIBRARY_PATH. This would be helpful for people who are building custom VMs that do not follow the same filesystem layout at the pharo.org one.

Pharo is already able to search LD_LIBRARY_PATH but this is being inhibited by an extra check that is specific to Iceberg:

This method is trying to detect whether to look for libgit2.so or libgit2.so.0 but if it cannot decide then it raises an error. I propose that instead of raising an error it could simply return ^ 'libgit2.so' as a default.