I tried to build Ruby on a system without libyaml today and realized
that my attempt from <https://github.com/ruby/psych/pull/557> doesn't
fix the error in <https://github.com/ruby/psych/issues/552>. I still got
the same `LoadError` from `digest` which stopped the build.
Since `LoadError` is not a `StandardError`, a plain `rescue` doesn't catch
it. Catch `LoadError` explicitly instead and reduce the scope of the
`begin` block.
I tested this change in a Ruby build on macOS without libyaml installed
and confirmed that `make` continues with a warning instead of aborting:
*** Following extensions are not compiled:
psych:
Could not be configured. It will not be installed.
...
This should address <https://bugs.ruby-lang.org/issues/18790>.
https://github.com/ruby/psych/commit/251289ba83
9357e310fb