This follows the design direction discussed on cfe-dev here:
The idea is that for C standard library builtins, even if the library
vendor chooses to annotate their routines with attribute((nonnull)),
we will ignore those attributes which pertain to pointer arguments that
have an associated size. This allows the widespread (and seemingly
reasonable) pattern of calling these routines with a null pointer and
a zero size. I have only done this for the library builtins currently
recognized by Clang, but we can now trivially add to this set. This will
be controllable with -fno-builtin if anyone should care to do so.
Note that this does *not* change the AST. As a consequence, warnings,
static analysis, and source code rewriting are not impacted.
This isn't even a regression on any platform as neither Clang nor LLVM
have ever put 'nonnull' onto these arguments for declarations. All this
patch does is enable it on other declarations while preventing us from
ever accidentally enabling it on these libc functions due to a library