Add Xcode file association for Fortran

Intel Fortran on Mac OS X enables Fortran support in Xcode.  This commit
teaches CMake to associate Fortran sources properly in Xcode projects.

See issue #9739.

Source/cmGlobalXCodeGenerator.cxx

@@ -655,6 +655,10 @@ cmGlobalXCodeGenerator::CreateXCodeFileReference(cmSourceFile* sf,
     {
     sourcecode += ".c.c";
     }
+  else if(lang && strcmp(lang, "Fortran") == 0)
+    {
+    sourcecode += ".fortran.f90";
+    }
   else if(ext == "png" || ext == "gif" || ext == "jpg")
     {
     sourcecode = "image";