[MS-ABI] Assign SEH handler indices to __try blocks
Assigns indices to try blocks. These indices will used in constructing 
tables that the mscrt function __except_handler3 reads during SEH.
Testing will occur once we actually emit the tables, in a subsequent 
patch.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213437 91177308-0d34-0410-b5e6-96231b3b80d8