Remove dead code; NFC

This code was added 17 years ago but never enabled or tested. GCC warns
that -I- is deprecated for them, and Clang gives an error when passed
-I-, so we may as well remove this code rather than hook it up to the
driver and maintain it.

Author: AaronBallman

clang/include/clang/Lex/HeaderSearch.h

@@ -247,16 +247,13 @@ class HeaderSearch {
   /// \#include search path information.  Requests for \#include "x" search the
   /// directory of the \#including file first, then each directory in SearchDirs
   /// consecutively. Requests for <x> search the current dir first, then each
-  /// directory in SearchDirs, starting at AngledDirIdx, consecutively.  If
-  /// NoCurDirSearch is true, then the check for the file in the current
-  /// directory is suppressed.
+  /// directory in SearchDirs, starting at AngledDirIdx, consecutively.
   std::vector<DirectoryLookup> SearchDirs;
   /// Whether the DirectoryLookup at the corresponding index in SearchDirs has
   /// been successfully used to lookup a file.
   std::vector<bool> SearchDirsUsage;
   unsigned AngledDirIdx = 0;
   unsigned SystemDirIdx = 0;
-  bool NoCurDirSearch = false;
 
   /// Maps HeaderMap keys to SearchDir indices. When HeaderMaps are used
   /// heavily, SearchDirs can start with thousands of HeaderMaps, so this Index
@@ -373,7 +370,7 @@ class HeaderSearch {
 
   /// Interface for setting the file search paths.
   void SetSearchPaths(std::vector<DirectoryLookup> dirs, unsigned angledDirIdx,
-                      unsigned systemDirIdx, bool noCurDirSearch,
+                      unsigned systemDirIdx,
                       llvm::DenseMap<unsigned, unsigned> searchDirToHSEntry);
 
   /// Add an additional search path.

clang/lib/Lex/HeaderSearch.cpp

@@ -105,15 +105,14 @@ void HeaderSearch::PrintStats() {
 
 void HeaderSearch::SetSearchPaths(
     std::vector<DirectoryLookup> dirs, unsigned int angledDirIdx,
-    unsigned int systemDirIdx, bool noCurDirSearch,
+    unsigned int systemDirIdx,
     llvm::DenseMap<unsigned int, unsigned int> searchDirToHSEntry) {
   assert(angledDirIdx <= systemDirIdx && systemDirIdx <= dirs.size() &&
          "Directory indices are unordered");
   SearchDirs = std::move(dirs);
   SearchDirsUsage.assign(SearchDirs.size(), false);
   AngledDirIdx = angledDirIdx;
   SystemDirIdx = systemDirIdx;
-  NoCurDirSearch = noCurDirSearch;
   SearchDirToHSEntry = std::move(searchDirToHSEntry);
   //LookupFileCache.clear();
   indexInitialHeaderMaps();
@@ -904,12 +903,12 @@ OptionalFileEntryRef HeaderSearch::LookupFile(
   ModuleMap::KnownHeader MSSuggestedModule;
   OptionalFileEntryRef MSFE;
 
-  // Unless disabled, check to see if the file is in the #includer's
-  // directory.  This cannot be based on CurDir, because each includer could be
-  // a #include of a subdirectory (#include "foo/bar.h") and a subsequent
-  // include of "baz.h" should resolve to "whatever/foo/baz.h".
-  // This search is not done for <> headers.
-  if (!Includers.empty() && !isAngled && !NoCurDirSearch) {
+  // Check to see if the file is in the #includer's directory. This cannot be
+  // based on CurDir, because each includer could be a #include of a
+  // subdirectory (#include "foo/bar.h") and a subsequent include of "baz.h"
+  // should resolve to "whatever/foo/baz.h". This search is not done for <>
+  // headers.
+  if (!Includers.empty() && !isAngled) {
     SmallString<1024> TmpDir;
     bool First = true;
     for (const auto &IncluderAndDir : Includers) {

clang/lib/Lex/InitHeaderSearch.cpp

@@ -513,9 +513,8 @@ void InitHeaderSearch::Realize(const LangOptions &Lang) {
   unsigned NonSystemRemoved = RemoveDuplicates(SearchList, NumQuoted, Verbose);
   NumAngled -= NonSystemRemoved;
 
-  bool DontSearchCurDir = false;  // TODO: set to true if -I- is set?
   Headers.SetSearchPaths(extractLookups(SearchList), NumQuoted, NumAngled,
-                         DontSearchCurDir, mapToUserEntries(SearchList));
+                         mapToUserEntries(SearchList));
 
   Headers.SetSystemHeaderPrefixes(SystemHeaderPrefixes);