Fix for bug 5691.

This fixes throwing exceptions inside @catch blocks nested inside outer @try blocks and also fixes jumping from an inner @finally to an outer @finally (via any relevant @catch blocks).

The code exhibiting this bug was based on code from CGObjCMac.  I believe that this bug may still be present on the Mac runtimes, although the test case in the bug contains a few GNUisms and won't compile without some minor tweaks with Apple's libobjc.

llvm-svn: 92117