[clang] [C] Disable use of NRVO (PR #101038)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> Instead of forcing this off for C compilations, how would you feel about instead changing the default for -felide-constructors to be off for C, so people can still re-enable the optimization to avoid performance / stack usage regressions? (Weird flag name for C, I know; maybe we should also think about adding an alias such as -felide-return-copies.)

I think that's a reasonable language dialect for users, and agree that the name should change. Thanks for the suggestion!

https://github.com/llvm/llvm-project/pull/101038