[CMake] Expose opt-remark tooling through libOptRemarks.dylib

* Create an install target for it
* Add it under tools/opt-remarks
* Add an export file for the dylib
* Install the llvm-c/OptRemarks.h header
* Add an API to query its version

rdar://45458839

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346127 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed