[llvm] [llvm] Use "= default" (NFC) (PR #166088)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> I had to remove (https://github.com/llvm/llvm-project/commit/a3c4fe2ce7446b2439acf7fb1ca6ad5f2fb229d3) one of these changes to fix a couple of our Flang builds.

This might be something specific to your setup. It looks like flang built fine in premerge with this configuration, and we use clang 21.x.

https://github.com/llvm/llvm-project/pull/166088