[clang] [Clang] Fixed an assertion caused by Microsoft integer literals exceeding the maximum value (PR #212743)

[Shengxin Pei via cfe-commits]

TPPPP72 wrote:

@frederick-vs-ja
For values > `18446744073709551615`, current Clang already emits an error, so no extra work is needed here. 
We should probably add new test cases with `-fsigned-char` and `-funsigned-char` to cover these behaviors properly.

(Note: If I recall correctly, `char` defaults to signed on x86 but unsigned on ARM/AArch64, so testing both flags explicitly makes a lot of sense.)

https://github.com/llvm/llvm-project/pull/212743