IncludeDirectories: Respect SYSTEM flag when using CONFIG genex.

Update the Makefile and Ninja generators to use the config when
requesting the include flags.

Source/cmMakefileTargetGenerator.cxx

@@ -1870,7 +1870,8 @@ void cmMakefileTargetGenerator::AddIncludeFlags(std::string& flags,
 
   std::string includeFlags =
     this->LocalGenerator->GetIncludeFlags(includes, this->GeneratorTarget,
-                                          lang, false, useResponseFile);
+                                          lang, false, useResponseFile,
+                                          config);
   if(includeFlags.empty())
     {
     return;

Source/cmNinjaTargetGenerator.cxx

@@ -170,8 +170,10 @@ cmNinjaTargetGenerator::ComputeFlagsForObject(cmSourceFile const* source,
     std::string includeFlags =
       this->LocalGenerator->GetIncludeFlags(includes, this->GeneratorTarget,
                                             language,
-      language == "RC" ? true : false); // full include paths for RC
+      language == "RC" ? true : false,  // full include paths for RC
                                         // needed by cmcldeps
+                                            false,
+                                            this->GetConfigName());
     if(cmGlobalNinjaGenerator::IsMinGW())
       cmSystemTools::ReplaceString(includeFlags, "\\", "/");
 

Tests/IncludeDirectories/SystemIncludeDirectories/CMakeLists.txt

@@ -14,8 +14,14 @@ target_include_directories(upstream SYSTEM PUBLIC
   $<TARGET_PROPERTY:systemlib,INTERFACE_INCLUDE_DIRECTORIES>
 )
 
+add_library(config_specific INTERFACE)
+set(testConfig ${CMAKE_BUILD_TYPE})
+target_include_directories(config_specific SYSTEM INTERFACE
+  "$<$<CONFIG:${testConfig}>:${CMAKE_CURRENT_SOURCE_DIR}/config_specific>"
+)
+
 add_library(consumer consumer.cpp)
-target_link_libraries(consumer upstream)
+target_link_libraries(consumer upstream config_specific)
 target_compile_options(consumer PRIVATE -Werror=unused-variable)
 
 add_library(iface IMPORTED INTERFACE)

Tests/IncludeDirectories/SystemIncludeDirectories/config_specific/config_iface.h

@@ -0,0 +1,14 @@
+
+#ifndef CONFIG_IFACE_H
+#define CONFIG_IFACE_H
+
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int configUnusedFunc()
+{
+  int unused;
+  return 0;
+}
+
+#endif

Tests/IncludeDirectories/SystemIncludeDirectories/consumer.cpp

@@ -1,6 +1,8 @@
 
 #include "upstream.h"
 
+#include "config_iface.h"
+
 int consumer()
 {
   return upstream();