Mark monitor functions `pure`/`nothrow` if possible.
Fix some `core.exception.*Error` functions attributes in modules.
Add issue 11461 workaround.

Issue URL: https://d.puremagic.com/issues/show_bug.cgi?id=11461
Merge pull request #635 from denis-sh/mark-some-monitor-functions-nothrow

[Trivial] Mark monitor functions `pure`/`nothrow` if possible.