[llvm] [clang] [SimplifyCFG] Not folding branch in loop header with constant iterations (PR #74268)

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xiangzh1 wrote:

Seems the check fail "dr2xx.cpp Line 1297: conversion from 'T' to 'unsigned long long' is ambiguous" has no relation with this change.

https://github.com/llvm/llvm-project/pull/74268