Added very lightweight, statically-allocated
counters for a variety of metrics associated
with expression parsing.  This should give some
idea of how much work the expression parser is
doing on Clang's behalf, and help with hopefully
reducing that load over time.

<rdar://problem/13210748> Audit type search/import for expressions


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@176714 91177308-0d34-0410-b5e6-96231b3b80d8