Do not explicitly report "standard" include directories as implicit

In commit 1293ed8507 (ParseImplicitIncludeInfo: keep implicit incl.
consistent when rerunning cmake, 2019-01-30, v3.14.0-rc1~26^2) we did
not account for `CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES`.  This
variable lets platform modules or toolchain files specify directories
that are to be explicitly passed as standard include directories.  These
include directories are used by the test project from which we extract
implicit include directories so they appear in the parsed results
whether or not the compiler really considers them implicit.  Exclude
these entries from the computed implicit include directories since they
are not actually implied by the compiler when we invoke it with
"standard" include directories passed explicitly.

Instead teach the build system generators to treat the "standard"
directories as implicit for purposes of excluding them from appearing
earlier in the compiler command line due to `include_directories` and
`target_include_directories` calls.

Issue: #18936, #18944

Modules/CMakeDetermineCompilerABI.cmake

@@ -96,6 +96,12 @@ function(CMAKE_DETERMINE_COMPILER_ABI lang src)
         file(APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
           "Parsed ${lang} implicit include dir info from above output: rv=${rv}\n${log}\n\n")
         if("${rv}" STREQUAL "done")
+          # Entries that we have been told to explicitly pass as standard include
+          # directories will not be implicitly added by the compiler.
+          if(CMAKE_${lang}_STANDARD_INCLUDE_DIRECTORIES)
+            list(REMOVE_ITEM implicit_incdirs ${CMAKE_${lang}_STANDARD_INCLUDE_DIRECTORIES})
+          endif()
+
           # We parsed implicit include directories, so override the default initializer.
           set(_CMAKE_${lang}_IMPLICIT_INCLUDE_DIRECTORIES_INIT "${implicit_incdirs}")
         endif()

Source/cmLocalGenerator.cxx

@@ -920,6 +920,20 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
     return result;
   }
 
+  // Standard include directories to be added unconditionally at the end.
+  // These are intended to simulate additional implicit include directories.
+  std::vector<std::string> userStandardDirs;
+  {
+    std::string key = "CMAKE_";
+    key += lang;
+    key += "_STANDARD_INCLUDE_DIRECTORIES";
+    std::string const value = this->Makefile->GetSafeDefinition(key);
+    cmSystemTools::ExpandListArgument(value, userStandardDirs);
+    for (std::string& usd : userStandardDirs) {
+      cmSystemTools::ConvertToUnixSlashes(usd);
+    }
+  }
+
   // Implicit include directories
   std::vector<std::string> implicitDirs;
   std::set<std::string> implicitSet;
@@ -929,14 +943,20 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
   };
   {
     // Raw list of implicit include directories
-    std::vector<std::string> impDirVec;
+    // Start with "standard" directories that we unconditionally add below.
+    std::vector<std::string> impDirVec = userStandardDirs;
 
     // Load implicit include directories for this language.
     std::string key = "CMAKE_";
     key += lang;
     key += "_IMPLICIT_INCLUDE_DIRECTORIES";
     if (const char* value = this->Makefile->GetDefinition(key)) {
+      size_t const impDirVecOldSize = impDirVec.size();
       cmSystemTools::ExpandListArgument(value, impDirVec);
+      // FIXME: Use cmRange with 'advance()' when it supports non-const.
+      for (size_t i = impDirVecOldSize; i < impDirVec.size(); ++i) {
+        cmSystemTools::ConvertToUnixSlashes(impDirVec[i]);
+      }
     }
 
     // The Platform/UnixPaths module used to hard-code /usr/include for C, CXX,
@@ -956,10 +976,8 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
     }
 
     for (std::string const& i : impDirVec) {
-      std::string imd = i;
-      cmSystemTools::ConvertToUnixSlashes(imd);
-      if (implicitSet.insert(imd).second) {
-        implicitDirs.emplace_back(std::move(imd));
+      if (implicitSet.insert(i).second) {
+        implicitDirs.emplace_back(i);
       }
     }
   }
@@ -998,21 +1016,10 @@ std::vector<BT<std::string>> cmLocalGenerator::GetIncludeDirectoriesImplicit(
   MoveSystemIncludesToEnd(result, config, lang, target);
 
   // Append standard include directories for this language.
-  {
-    std::vector<std::string> userStandardDirs;
-    {
-      std::string key = "CMAKE_";
-      key += lang;
-      key += "_STANDARD_INCLUDE_DIRECTORIES";
-      std::string const value = this->Makefile->GetSafeDefinition(key);
-      cmSystemTools::ExpandListArgument(value, userStandardDirs);
-    }
-    userDirs.reserve(userDirs.size() + userStandardDirs.size());
-    for (std::string& usd : userStandardDirs) {
-      cmSystemTools::ConvertToUnixSlashes(usd);
-      emitDir(usd);
-      userDirs.emplace_back(std::move(usd));
-    }
+  userDirs.reserve(userDirs.size() + userStandardDirs.size());
+  for (std::string& usd : userStandardDirs) {
+    emitDir(usd);
+    userDirs.emplace_back(std::move(usd));
   }
 
   // Append compiler implicit include directories