Work around a build issue with MSVC; NFC (#142195)

Microsoft helpfully defines `THIS` to `void` in two different platform
SDK headers, at least one of which is reachable via <Windows.h>. We have
a user who ran into a build because of `THIS` unfortunate macro name
collision.

Rename the members to better match our naming conventions.

Fixes #142186

Author: AaronBallman

clang/include/clang/Basic/Attr.td

@@ -1997,10 +1997,12 @@ private:
   ArrayRef<SourceLocation> ArgLocs;
 
 public:
-  static constexpr int THIS = 0;
-  static constexpr int INVALID = -1;
-  static constexpr int UNKNOWN = -2;
-  static constexpr int GLOBAL = -3;
+  enum ArgIndex {
+    This = 0,
+    Invalid = -1,
+    Unknown = -2,
+    Global = -3,
+  };
 
   void setArgs(ArrayRef<IdentifierInfo*> Idents, ArrayRef<SourceLocation> Locs) {
     assert(Idents.size() == params_Size);

clang/lib/Sema/CheckExprLifetime.cpp

@@ -665,7 +665,7 @@ static void visitFunctionCallArguments(IndirectLocalPath &Path, Expr *Call,
                  CanonCallee->getParamDecl(I)->getAttr<LifetimeCaptureByAttr>();
              CaptureAttr && isa<CXXConstructorDecl>(CanonCallee) &&
              llvm::any_of(CaptureAttr->params(), [](int ArgIdx) {
-               return ArgIdx == LifetimeCaptureByAttr::THIS;
+               return ArgIdx == LifetimeCaptureByAttr::This;
              }))
       // `lifetime_capture_by(this)` in a class constructor has the same
       // semantics as `lifetimebound`:

clang/lib/Sema/SemaAttr.cpp

@@ -290,7 +290,7 @@ void Sema::inferLifetimeCaptureByAttribute(FunctionDecl *FD) {
       // pointer-like reference types (`const T&`, `T&&`).
       if (PVD->getType()->isReferenceType() &&
           sema::isGLSPointerType(PVD->getType().getNonReferenceType())) {
-        int CaptureByThis[] = {LifetimeCaptureByAttr::THIS};
+        int CaptureByThis[] = {LifetimeCaptureByAttr::This};
         PVD->addAttr(
             LifetimeCaptureByAttr::CreateImplicit(Context, CaptureByThis, 1));
       }

clang/lib/Sema/SemaChecking.cpp

@@ -3333,8 +3333,8 @@ void Sema::checkLifetimeCaptureBy(FunctionDecl *FD, bool IsMemberFunction,
   if (!FD || Args.empty())
     return;
   auto GetArgAt = [&](int Idx) -> const Expr * {
-    if (Idx == LifetimeCaptureByAttr::GLOBAL ||
-        Idx == LifetimeCaptureByAttr::UNKNOWN)
+    if (Idx == LifetimeCaptureByAttr::Global ||
+        Idx == LifetimeCaptureByAttr::Unknown)
       return nullptr;
     if (IsMemberFunction && Idx == 0)
       return ThisArg;
@@ -3349,7 +3349,7 @@ void Sema::checkLifetimeCaptureBy(FunctionDecl *FD, bool IsMemberFunction,
     for (int CapturingParamIdx : Attr->params()) {
       // lifetime_capture_by(this) case is handled in the lifetimebound expr
       // initialization codepath.
-      if (CapturingParamIdx == LifetimeCaptureByAttr::THIS &&
+      if (CapturingParamIdx == LifetimeCaptureByAttr::This &&
           isa<CXXConstructorDecl>(FD))
         continue;
       Expr *Capturing = const_cast<Expr *>(GetArgAt(CapturingParamIdx));

clang/lib/Sema/SemaDeclAttr.cpp

@@ -4155,7 +4155,7 @@ LifetimeCaptureByAttr *Sema::ParseLifetimeCaptureByAttr(const ParsedAttr &AL,
   }
   if (!IsValid)
     return nullptr;
-  SmallVector<int> FakeParamIndices(N, LifetimeCaptureByAttr::INVALID);
+  SmallVector<int> FakeParamIndices(N, LifetimeCaptureByAttr::Invalid);
   auto *CapturedBy =
       LifetimeCaptureByAttr::Create(Context, FakeParamIndices.data(), N, AL);
   CapturedBy->setArgs(ParamIdents, ParamLocs);
@@ -4198,8 +4198,8 @@ void Sema::LazyProcessLifetimeCaptureByParams(FunctionDecl *FD) {
   if (Attrs.empty())
     return;
   llvm::StringMap<int> NameIdxMapping = {
-      {"global", LifetimeCaptureByAttr::GLOBAL},
-      {"unknown", LifetimeCaptureByAttr::UNKNOWN}};
+      {"global", LifetimeCaptureByAttr::Global},
+      {"unknown", LifetimeCaptureByAttr::Unknown}};
   int Idx = 0;
   if (HasImplicitThisParam) {
     NameIdxMapping["this"] = 0;