Fix for eldoc-mode for ClojureCLR

[dotemacs]

When using the REPL, whenever you'd type the function name, because
Throwable is JVM specific, eldoc-mode would try to look up the
function and when it wouldn't find it, it would bomb out with the
complaint that Throwable wasn't defined. Which is to be expected since
it's not running on JVM.

Looking at the documentation
https://docs.oracle.com/javase/10/docs/api/java/lang/Throwable.html

The Throwable class is the superclass of all errors and exceptions in the Java language.

And in C#, Exception
https://docs.microsoft.com/en-us/dotnet/api/system.exception?redirectedfrom=MSDN&view=netframework-4.8

This class is the base class for all exceptions.

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Thanks!

[bbatsov]

Nice! Thanks for fixing this. I never thought that inf-clojure might be a good option for ClojureCLR users.