Do not treat DEFINITIONS as a built-in directory property

Add policy CMP0059 to cover this change.  The property has been
deprecated since CMake 2.4 anyway.

This will help clean up cmMakefile -- the DefineFlagsOrig member should
not need to exist.

Source/cmMakefile.cxx

@@ -4209,8 +4209,19 @@ const char *cmMakefile::GetProperty(const std::string& prop,
     }
   else if (prop == "DEFINITIONS")
     {
-    output += this->DefineFlagsOrig;
-    return output.c_str();
+    switch(this->GetPolicyStatus(cmPolicies::CMP0059))
+      {
+      case cmPolicies::WARN:
+          this->IssueMessage(cmake::AUTHOR_WARNING, this->GetPolicies()->
+                             GetPolicyWarning(cmPolicies::CMP0059));
+      case cmPolicies::OLD:
+        output += this->DefineFlagsOrig;
+        return output.c_str();
+      case cmPolicies::NEW:
+      case cmPolicies::REQUIRED_ALWAYS:
+      case cmPolicies::REQUIRED_IF_USED:
+        break;
+      }
     }
   else if (prop == "LINK_DIRECTORIES")
     {

Source/cmPolicies.cxx

@@ -385,6 +385,11 @@ cmPolicies::cmPolicies()
     CMP0058, "CMP0058",
     "Ninja requires custom command byproducts to be explicit.",
     3,3,0, cmPolicies::WARN);
+
+  this->DefinePolicy(
+    CMP0059, "CMP0059",
+    "Do no treat DEFINITIONS as a built-in directory property.",
+    3,3,0, cmPolicies::WARN);
 }
 
 cmPolicies::~cmPolicies()

Source/cmPolicies.h

@@ -116,6 +116,8 @@ public:
     CMP0057, ///< Disallow multiple MAIN_DEPENDENCY specifications
     /// for the same file.
     CMP0058, ///< Ninja requires custom command byproducts to be explicit
+    CMP0059, ///< Do not treat ``DEFINITIONS`` as a built-in directory
+    /// property.
 
     /** \brief Always the last entry.
      *