[Frontend] Remove ShowIncludesPretendHeader

[smeenai]

Summary

It hasn't been written to since https://reviews.llvm.org/D46652, so it
was always empty. I don't have enough context on that diff to know if
the removal of the write to ShowIncludesPretendHeader in that diff was
intentional, but no one's complained about it for five years, so I
assume we're okay to just get rid of it entirely.

[hans]

lgtm

clang/include/clang/Frontend/DependencyOutputOptions.h

public:
   /// A list of names to use as the targets in the dependency file; this list
   /// must contain at least one entry.
   std::vector<std::string> Targets;
 
   /// A list of extra dependencies (filename and kind) to be used for every
   /// target.
   std::vector<std::pair<std::string, ExtraDepKind>> ExtraDeps;
 
-  /// In /showIncludes mode, pretend the main TU is a header with this name.
-  std::string ShowIncludesPretendHeader;
-
   /// The file to write GraphViz-formatted header dependencies to.
   std::string DOTOutputFile;
 
   /// The directory to copy module dependencies to when collecting them.
   std::string ModuleDependencyOutputDir;
 
 public:
   DependencyOutputOptions()

clang/lib/Frontend/HeaderIncludeGen.cpp

void HeaderIncludesCallback::FileChanged(SourceLocation Loc,
   if (Reason == PPCallbacks::EnterFile) {
     ++CurrentIncludeDepth;
   } else if (Reason == PPCallbacks::ExitFile) {
     if (CurrentIncludeDepth)
       --CurrentIncludeDepth;
 
     // We track when we are done with the predefines by watching for the first
     // place where we drop back to a nesting depth of 1.
-    if (CurrentIncludeDepth == 1 && !HasProcessedPredefines) {
-      if (!DepOpts.ShowIncludesPretendHeader.empty()) {
-        PrintHeaderInfo(OutputFile, DepOpts.ShowIncludesPretendHeader,
-                        ShowDepth, 2, MSStyle);
-      }
+    if (CurrentIncludeDepth == 1 && !HasProcessedPredefines)
       HasProcessedPredefines = true;
-    }
 
     return;
   } else {
     return;
   }
 
   if (!ShouldShowHeader(NewFileType))
     return;
 
   unsigned IncludeDepth = CurrentIncludeDepth;
   if (!HasProcessedPredefines)
     --IncludeDepth; // Ignore indent from <built-in>.
-  else if (!DepOpts.ShowIncludesPretendHeader.empty())
-    ++IncludeDepth; // Pretend inclusion by ShowIncludesPretendHeader.
 
   // FIXME: Identify headers in a more robust way than comparing their name to
   // "<command line>" and "<built-in>" in a bunch of places.
   if (Reason == PPCallbacks::EnterFile &&
       UserLoc.getFilename() != StringRef("<command line>")) {
     PrintHeaderInfo(OutputFile, UserLoc.getFilename(), ShowDepth, IncludeDepth,
                     MSStyle);
   }