[clang] [clang] Ignore GCC 11 `[[malloc(x)]]` attribute (PR #68059)

[Erich Keane via cfe-commits]

erichkeane wrote:

Closing, as I separately submitted this with my changes here: [79a28aa](https://github.com/llvm/llvm-project/commit/79a28aa0a48feba34ddc3c1791ea0be88f354542)

Note original author should be in tact.  Thank you for your contribution!

https://github.com/llvm/llvm-project/pull/68059