Detection of out-of-process JIT support takes non-trivial time on each lit invocation

[Endilll]

As reported in #144064, this PR added some non-trivial overhead to lit invocations, making development cycle significantly longer.

It was suggested to compute this once and put in some kind of cache to prevent re-evaluations, maybe some lit cache or even CMake, but 22 seconds I measured is still a long time.

[vgvassilev]

cc: @SahilPatidar

[shafik]

I am assuming we see this on the build bots as well? How much longer are builds on bots taking since this change? Is this increase in time something we can catch during pre-commi?

[vgvassilev]

I am assuming we see this on the build bots as well? How much longer are builds on bots taking since this change? Is this increase in time something we can catch during pre-commi?

No, this is amortized when the tests are many. The problem is when we run only a couple of tests it becomes dominant.