[pp-trace] Add PragmaOnce callback

[KyleFromKitware]

Rebased onto main for D141000.

clang-tools-extra/pp-trace/PPCallbacksTracker.h

public:
   void PragmaWarningPush(PragmaIntroducer Introducer, SourceLocation Loc,
                          int Level) override;
   void PragmaWarningPop(PragmaIntroducer Introducer,
                         SourceLocation Loc) override;
   void PragmaExecCharsetPush(PragmaIntroducer Introducer, SourceLocation Loc,
                              StringRef Str) override;
   void PragmaExecCharsetPop(PragmaIntroducer Introducer,
                             SourceLocation Loc) override;
+  void PragmaOnce(PragmaIntroducer Introducer, SourceLocation Loc) override;
   void MacroExpands(const Token &MacroNameTok, const MacroDefinition &MD,
                     SourceRange Range, const MacroArgs *Args) override;
   void MacroDefined(SourceLocation HashLoc, const Token &MacroNameTok,
                     const MacroDirective *MD) override;
   void MacroUndefined(SourceLocation HashLoc, const Token &MacroNameTok,
                       const MacroDefinition &MD,
                       const MacroDirective *Undef) override;
   void Defined(const Token &MacroNameTok, const MacroDefinition &MD,

clang-tools-extra/pp-trace/PPCallbacksTracker.cpp

 // is read.
 void PPCallbacksTracker::PragmaExecCharsetPop(PragmaIntroducer Introducer,
                                               SourceLocation Loc) {
   beginCallback("PragmaExecCharsetPop");
   appendArgument("Introducer", Introducer);
   appendArgument("Loc", Loc);
 }
 
+/// Callback invoked when a \#pragma once directive is read.
+void PPCallbacksTracker::PragmaOnce(PragmaIntroducer Introducer,
+                                    SourceLocation Loc) {
+  beginCallback("PragmaOnce");
+  appendArgument("Introducer", Introducer);
+  appendArgument("Loc", Loc);
+}
+
 // Called by Preprocessor::HandleMacroExpandedIdentifier when a
 // macro invocation is found.
 void PPCallbacksTracker::MacroExpands(const Token &MacroNameTok,
                                       const MacroDefinition &MacroDefinition,
                                       SourceRange Range,
                                       const MacroArgs *Args) {
   beginCallback("MacroExpands");
   appendArgument("MacroNameTok", MacroNameTok);

clang-tools-extra/test/pp-trace/pp-trace-pragma-general.cpp

-// RUN: pp-trace -callbacks '*,-FileChanged,-MacroDefined' %s -- | FileCheck --strict-whitespace %s
+// RUN: pp-trace -callbacks '*,-FileChanged,-MacroDefined' -extra-arg-before=-xc++-header %s -- | FileCheck --strict-whitespace %s
 
 #pragma clang diagnostic push
 #pragma clang diagnostic pop
 #pragma clang diagnostic ignored "-Wformat"
 #pragma clang diagnostic warning "-Wformat"
 #pragma clang diagnostic error "-Wformat"
 #pragma clang diagnostic fatal "-Wformat"
 
 #pragma GCC diagnostic push
 #pragma GCC diagnostic pop
 #pragma GCC diagnostic ignored "-Wformat"
 #pragma GCC diagnostic warning "-Wformat"
 #pragma GCC diagnostic error "-Wformat"
 #pragma GCC diagnostic fatal "-Wformat"
 
 void foo() {
 #pragma clang __debug captured
 { }
 }
 
+#pragma once
+
 // CHECK: ---
 // CHECK-NEXT: - Callback: PragmaDirective
 // CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:3:1", Kind: PIK_HashPragma}
 // CHECK-NEXT: - Callback: PragmaDiagnosticPush
 // CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:3:1", Kind: PIK_HashPragma}
 // CHECK-NEXT:   Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:3:15"
 // CHECK-NEXT:   Namespace: clang
 // CHECK-NEXT: - Callback: PragmaDirective

 // CHECK-NEXT:   Mapping: MAP_FATAL
 // CHECK-NEXT:   Str: -Wformat
 // CHECK-NEXT: - Callback: PragmaDirective
 // CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:18:1", Kind: PIK_HashPragma}
 // CHECK-NEXT: - Callback: PragmaDebug
 // CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:18:1", Kind: PIK_HashPragma}
 // CHECK-NEXT:   Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:18:23"
 // CHECK-NEXT:   DebugType: captured
+// CHECK-NEXT: - Callback: PragmaDirective
+// CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:22:1", Kind: PIK_HashPragma}
+// CHECK-NEXT: - Callback: PragmaOnce
+// CHECK-NEXT:   Introducer: {Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:22:1", Kind: PIK_HashPragma}
+// CHECK-NEXT:   Loc: "{{.*}}{{[/\\]}}pp-trace-pragma-general.cpp:22:9"
 // CHECK-NEXT: - Callback: EndOfMainFile
 // CHECK-NEXT: ...