Make DiagnosticErrorTrap keep a count of the errors that occurred so multiple
DiagnosticErrorTraps can be composed (e.g. a trap inside another trap).

Fixes http://llvm.org/PR10462 & rdar://9852007.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@136447 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed