swift234

[sil-inliner] Add a check to inlineFunction to prevent circular inlining.

Circular inlining will lead to infinite instruction creation by the SILCloner.

I believe this check was not added before since before the performance inliner
the only user was MandatoryInlining which performed this check before
recursively processing the callee function for inlining purposes.

Swift SVN r11435