Reland [Clang] Make the SizeType, SignedSizeType and PtrdiffType be named sugar types (#149613)

The checks for the 'z' and 't' format specifiers added in the original
PR #143653 had some issues and were overly strict, causing some build
failures and were consequently reverted at
https://github.com/llvm/llvm-project/commit/4c85bf2fe8042c855c9dd5be4b02191e9d071ffd.

In the latest commit
https://github.com/llvm/llvm-project/pull/149613/commits/27c58629ec76a703fde9c0b99b170573170b4a7a,
I relaxed the checks for the 'z' and 't' format specifiers, so warnings
are now only issued when they are used with mismatched types.

The original intent of these checks was to diagnose code that assumes
the underlying type of `size_t` is `unsigned` or `unsigned long`, for
example:

```c
printf("%zu", 1ul); // Not portable, but not an error when size_t is unsigned long
```  

However, it produced a significant number of false positives. This was
partly because Clang does not treat the `typedef` `size_t` and
`__size_t` as having a common "sugar" type, and partly because a large
amount of existing code either assumes `unsigned` (or `unsigned long`)
is `size_t`, or they define the equivalent of size_t in their own way
(such as
sanitizer_internal_defs.h).https://github.com/llvm/llvm-project/blob/2e67dcfdcd023df2f06e0823eeea23990ce41534/compiler-rt/lib/sanitizer_common/sanitizer_internal_defs.h#L203

1 files changed, 2 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 0fda31c..ab345a5 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -720,7 +720,7 @@ static bool matchesStlAllocatorFn(const Decl *D, const ASTContext &Ctx) {
       (MD->getNumParams() != 1 && MD->getNumParams() != 2))
     return false;
 
-  if (MD->parameters()[0]->getType().getCanonicalType() != Ctx.getSizeType())
+  if (!Ctx.hasSameType(MD->parameters()[0]->getType(), Ctx.getSizeType()))
     return false;
 
   if (MD->getNumParams() == 2) {
@@ -2491,6 +2491,7 @@ void CodeGenFunction::EmitVariablyModifiedType(QualType type) {
     case Type::ObjCObjectPointer:
     case Type::BitInt:
     case Type::HLSLInlineSpirv:
+    case Type::PredefinedSugar:
       llvm_unreachable("type class is never variably-modified!");
 
     case Type::Elaborated: