Factor out enum MessageType into dedicated header

Reduce the number of files relying on `cmake.h`.

Source/cmTargetCompileOptionsCommand.cxx

@@ -7,8 +7,8 @@
 #include "cmAlgorithms.h"
 #include "cmListFileCache.h"
 #include "cmMakefile.h"
+#include "cmMessageType.h"
 #include "cmTarget.h"
-#include "cmake.h"
 
 class cmExecutionStatus;
 
@@ -24,7 +24,7 @@ void cmTargetCompileOptionsCommand::HandleMissingTarget(
   std::ostringstream e;
   e << "Cannot specify compile options for target \"" << name
     << "\" which is not built by this project.";
-  this->Makefile->IssueMessage(cmake::FATAL_ERROR, e.str());
+  this->Makefile->IssueMessage(MessageType::FATAL_ERROR, e.str());
 }
 
 std::string cmTargetCompileOptionsCommand::Join(