[clang] [clang] Add clang::preferred_type attribute for bitfields (PR #69104)

[Erich Keane via cfe-commits]

erichkeane wrote:

Ah, found it: https://godbolt.org/z/59sc87Y3Y

See how on the assignment to a bitfield we check to make sure the largest value of the enum will fit in the bitfield?  I'm saying I want us to do this EARLIER, on declaration with this attribute.

https://github.com/llvm/llvm-project/pull/69104