[clang] [llvm] [clang] Support multiple in-process cc1 jobs in a ToolSession (PR #222531)

[Anutosh Bhat via cfe-commits]

anutosh491 wrote:

Sorry @aganea, @rnk 

Had lost some momentum on this but I'm back again trying to have the couple major PRs supporting my RFC merged.
This being one of them !

I've tried addressing the reviews from above. 

I've added  a `canRunAgain()`  mechanism so we stop further in-process jobs after a recovered compiler crash. Normal compilation errors still allow reuse, and I've addressed the fatal-error handler and time-trace cleanup issues too.

https://github.com/llvm/llvm-project/pull/222531