Worked on SpinLock (INCOMPLETE)

Added basic Spinlock to Korlib.
Added Test instruction to TinySimulator.
Added SpinLock internal intrinsic compiler replacement.
Updated ReplacementTargetAttribute to allow multiple uses.
Merge remote-tracking branch 'origin/master' into spinlock
Fix issue from upstream merge.
Finished implementing SpinLock.

Finished implementing a rudimentary version of SpinLock that does not
follow .NET spec.
Also shifted the PlatformIntrinsicTransformationStage to run after the
IRTransformationStage.
Merge pull request #34 from charsleysa/spinlock

Implemented rudimentary Spinlock
Fix TestWorld failing.
Merge pull request #35 from charsleysa/spinlock

Fix TestWorld failing.
Merge remote-tracking branch 'upstream/master'