BUG: Don't generate build rules for header files.

Source/cmBorlandMakefileGenerator.cxx

@@ -178,7 +178,11 @@ OutputBuildObjectFromSource(std::ostream& fout,
                             const cmSourceFile& source,
                             const char* extraCompileFlags,
                             bool shared)
-{ 
+{
+  // Header files shouldn't have build rules.
+  if(source.IsAHeaderFileOnly())
+    return;
+
   std::string comment = "Build ";
   std::string objectFile = std::string(shortName) + 
     this->GetOutputExtension(source.GetSourceExtension().c_str());

Source/cmNMakeMakefileGenerator.cxx

@@ -356,6 +356,10 @@ OutputBuildObjectFromSource(std::ostream& fout,
                             const char* extraCompileFlags,
                             bool shared)
 { 
+  // Header files shouldn't have build rules.
+  if(source.IsAHeaderFileOnly())
+    return;
+
   std::string comment = "Build ";
   std::string objectFile = std::string(shortName) + 
     this->GetOutputExtension(source.GetSourceExtension().c_str());

Source/cmUnixMakefileGenerator.cxx

@@ -1594,7 +1594,10 @@ OutputBuildObjectFromSource(std::ostream& fout,
                             const char* extraCompileFlags,
                             bool shared)
 {
-            
+  // Header files shouldn't have build rules.
+  if(source.IsAHeaderFileOnly())
+    return;
+
   std::string comment = "Build ";
   std::string objectFile = std::string(shortName) + m_ObjectFileExtension;
   comment += objectFile + "  From ";