Resolve "Add a gdk doctor diagnostic when the icu4c package is bad"

What does this Merge Request do?

This MR introduces a Golang diagnostic. It currently only detects if Golang can build binaries that depend upon the icu4c package.

$ gdk doctor
(in /Users/ash/src/gdk/gdk-primary)
================================================================================
Please note these warning only exist for debugging purposes and can
help you when you encounter issues with GDK.
If your GDK is working fine, you can safely ignore them. Thanks!
================================================================================


Golang
--------------------------------------------------------------------------------
Golang is current unable to build binaries that use the icu4c package. 
You can try the following to fix:

go clean -cache

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.

Closes #880 (closed)