[libclang] Record code-completion invocations to a temporary file when
requested by client

This is a follow up to r319702 which records parsing invocations.

These files are not emitted by default, and the client has to specify the
invocation emission path first.

rdar://35322543

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@320085 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit 8c8d967b8ab952e6072fb9aeea995fb87dd3a806)
7 files changed