ENH: Re-enable system include dir suppression

This creates variable CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES to
specify implicit include directories on a per-language basis.  This
replaces the previous platform-wide variable.  It is necessary to
avoid explicit specification of -I/usr/include on some compilers
(such as HP aCC) because:

  1.) It may break ordering among system include directories defined
      internally by the compiler, thus getting wrong system headers.
  2.) It tells the compiler to treat the system include directory
      as a user include directory, enabling warnings in the headers.

See issue #8598.

1 files changed, 9 insertions, 0 deletions

diff --git a/Source/cmDocumentVariables.cxx b/Source/cmDocumentVariables.cxx
index 02f1d6a..27afd92 100644
--- a/Source/cmDocumentVariables.cxx
+++ b/Source/cmDocumentVariables.cxx
@@ -1097,6 +1097,15 @@ void cmDocumentVariables::DefineVariables(cmake* cm)
      "This is a list of file extensions that may be "
      "part of a project for a given language but are not compiled. ",false,
      "Variables for Languages");
+
+  cm->DefineProperty
+    ("CMAKE_<LANG>_IMPLICIT_INCLUDE_DIRECTORIES", cmProperty::VARIABLE,
+     "Directories implicitly searched by the compiler for header files.",
+     "CMake does not explicitly specify these directories on compiler "
+     "command lines for language <LANG>.  "
+     "This prevents system include directories from being treated as user "
+     "include directories on some compilers.", false,
+     "Variables for Languages");
   
   cm->DefineProperty
     ("CMAKE_<LANG>_LINKER_PREFERENCE", cmProperty::VARIABLE,