[Docs][Clang][Attr] mark no_stack_protector+no_sanitize GCC compatible

[nickdesaulniers]

Summary

GCC has supported the function attributes
attribute((no_stack_protector)) since GCC 11 and
attribute((no_sanitize(""))) since GCC 8.

Signed-off-by: Nick Desaulniers <[e-mail]>

[melver]

There might be subtle inconsistencies between values accepted by our no_sanitize and GCC's no_sanitize, because of internal naming differences, but I couldn't say what those are right now (I think no_sanitize("coverage") only works with Clang, and GCC wants no_sanitize_coverage which we don't have due to not allowing new no_sanitize_*).

[aaron.ballman]

This change breaks code by removing the [[clang::no_sanitize]] spelling (and the fact that zero tests broke show we're missing test coverage here). We don't currently have a spelling to represent an attribute known to both Clang and GCC, nor do we currently have any attributes that use both the Clang and GCC spellings (which both include a GNU spelling that would be duplicated). I think you should keep the Clang spelling, add a GCC spelling, make sure that ClangAttrEmitter.cpp does not generate two GNU spellings for it, and add some basic test coverage for the change.

[nickdesaulniers]

ah, ok, then if this isn't a quick cleanup, I don't really care about this.

[aaron.ballman]

In D104491#2827730, @nickdesaulniers wrote:

ah, ok, then if this isn't a quick cleanup, I don't really care about this.

I took a quick look at ClangAttrEmitter.cpp, and it looks like the only change that is needed is within the GetFlattenedSpelling() function. So not quite quick, but shouldn't be too bad (in case someone wants to pick this back up).

clang/include/clang/Basic/Attr.td

def NotTailCalled : InheritableAttr {
   let Spellings = [Clang<"not_tail_called">];
   let Subjects = SubjectList<[Function]>;
   let Documentation = [NotTailCalledDocs];
   let SimpleHandler = 1;
 }
 def : MutualExclusions<[AlwaysInline, NotTailCalled]>;
 
 def NoStackProtector : InheritableAttr {
-  let Spellings = [Clang<"no_stack_protector">];
+  let Spellings = [GCC<"no_stack_protector">];
   let Subjects = SubjectList<[Function]>;
   let Documentation = [NoStackProtectorDocs];
   let SimpleHandler = 1;
 }
 
 def NoThrow : InheritableAttr {
   let Spellings = [GCC<"nothrow">, Declspec<"nothrow">];
   let Subjects = SubjectList<[FunctionLike]>;
def X86ForceAlignArgPointer : InheritableAttr, TargetSpecificAttr<TargetAnyX86> {
   let Spellings = [GCC<"force_align_arg_pointer">];
   // Technically, this appertains to a FunctionDecl, but the target-specific
   // code silently allows anything function-like (such as typedefs or function
   // pointers), but does not apply the attribute to them.
   let Documentation = [X86ForceAlignArgPointerDocs];
 }
 
 def NoSanitize : InheritableAttr {
-  let Spellings = [Clang<"no_sanitize">];
+  let Spellings = [GCC<"no_sanitize">];
   let Args = [VariadicStringArgument<"Sanitizers">];
   let Subjects = SubjectList<[Function, ObjCMethod, GlobalVar], ErrorDiag>;
   let Documentation = [NoSanitizeDocs];
   let AdditionalMembers = [{
     SanitizerMask getMask() const {
       SanitizerMask Mask;
       for (auto SanitizerName : sanitizers()) {
         SanitizerMask ParsedMask =