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

[Ding Fei via cfe-commits]

danix800 wrote:

> @danix800 Could you please have a look at the failed test, such that we could reapply this PR? I reverted this soon after I realized the broken test is from this PR.

The test randomly fails for unknown reason, on VS2019~2022, after 1c154bd755153b5c6ada4bbed58facf23f6abffc (seems totally irrelevant to this randomness). Not sure if it's a compiler bug.

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