[runtime] Fix a nullref when casting a null object to a complex type when using --debug=casts. Fixes #14552/#14493.
Suggestion fix for bug https://bugzilla.xamarin.com/show_bug.cgi?id=6327
[runtime] Make suspend work during thread cleanup. Fixes #14555

SDB does suspend/resume during thread cleanup. It used to work until I introduced
critical regions. This won't work anymore as we need to lookup the thread info object
and during cleanup it will be gone.

The fix is to introduce mono_thread_info_current_slow which is a variant of
mono_thread_info_current that does search the thread list if the TLS key
is gone.
[runtime] Fix a loader leak in the aot compiler.
Merge pull request #755 from ondrejmyska/master

Suggestion fix for bug https://bugzilla.xamarin.com/show_bug.cgi?id=6327
[verifier]Check generic constraints for duplicates. Fixes #1782.
Add System.ServiceModel.Activation assembly. Fixes #14544
Don't emit inflated type parameter constraints which can collide with special constraint types.
Don't set sealed flag for imported static types
Bump ikvm
Improve the build system.
Fix the OSX and Windows build.