Silence spurious -Wnontrivial-memcall warnings in C mode (#137429)

clang currently issues a warning when memset is used on a struct that
contains an address-discriminated pointer field, even though this is
entirely valid behavior.

For example:

```
struct S {
  int * __ptrauth(1, 1, 100) p;
} s;

memset(&s, 0, sizeof(struct S));
```

Only allow the warning to be emitted in C++ mode to silence the warning.

rdar://142495870

1 files changed, 5 insertions, 5 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 018d121..d2cad8a 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -9735,9 +9735,9 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
       // completed later. GCC does not diagnose such code, but we may want to
       // consider diagnosing it in the future, perhaps under a different, but
       // related, diagnostic group.
-      bool MayBeTriviallyCopyableCXXRecord =
-          RT->isIncompleteType() ||
-          RT->desugar().isTriviallyCopyableType(Context);
+      bool NonTriviallyCopyableCXXRecord =
+          getLangOpts().CPlusPlus && !RT->isIncompleteType() &&
+          !RT->desugar().isTriviallyCopyableType(Context);
 
       if ((BId == Builtin::BImemset || BId == Builtin::BIbzero) &&
           RT->getDecl()->isNonTrivialToPrimitiveDefaultInitialize()) {
@@ -9746,7 +9746,7 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
                                 << ArgIdx << FnName << PointeeTy << 0);
         SearchNonTrivialToInitializeField::diag(PointeeTy, Dest, *this);
       } else if ((BId == Builtin::BImemset || BId == Builtin::BIbzero) &&
-                 !MayBeTriviallyCopyableCXXRecord && ArgIdx == 0) {
+                 NonTriviallyCopyableCXXRecord && ArgIdx == 0) {
         // FIXME: Limiting this warning to dest argument until we decide
         // whether it's valid for source argument too.
         DiagRuntimeBehavior(Dest->getExprLoc(), Dest,
@@ -9759,7 +9759,7 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
                                 << ArgIdx << FnName << PointeeTy << 1);
         SearchNonTrivialToCopyField::diag(PointeeTy, Dest, *this);
       } else if ((BId == Builtin::BImemcpy || BId == Builtin::BImemmove) &&
-                 !MayBeTriviallyCopyableCXXRecord && ArgIdx == 0) {
+                 NonTriviallyCopyableCXXRecord && ArgIdx == 0) {
         // FIXME: Limiting this warning to dest argument until we decide
         // whether it's valid for source argument too.
         DiagRuntimeBehavior(Dest->getExprLoc(), Dest,