[clang] [analyzer][Solver] Early return if sym is concrete on assuming (PR #115579)

[Ding Fei via cfe-commits]

danix800 wrote:

> Thank you for your dedication. What are your plans? Do you plan to continue pushing this?
> 
> Btw why did this test only fail on Windows?

I'll further investigate if it's possilbe to do similar improvement on the solver in other ways.

https://github.com/llvm/llvm-project/pull/115579