[clang] [clang] increase default constexpr step limit (PR #143785)

[via cfe-commits]

Sirraide wrote:

> on my machine 20 million steps take roughly 10 seconds.

Yeah, same.

Added some more reviewers in case anyone can think of a reason why we *shouldn’t* do this.

https://github.com/llvm/llvm-project/pull/143785