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

[Jens Gustedt via cfe-commits]

gustedt wrote:

I see that the fix is almost ready, good. But generally it would also have helped if the `__has_c_attribute` feature test for this type of borrowed attributes would provide means to distinguish different versions. Here gcc as well as clang only have the value 1. So if the patch would also change the return value for clang to the year whenever the first version of gcc-11 with that feature was released, that would really be helpful.

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