automoc: Read target defines unconditionally

Commit 429e3699 (Process COMPILE_DEFINITIONS as generator expressions
in QtAutomoc., 2013-01-25) introduced a check for the existence of the
COMPILE_DEFINITIONS property on the target before processing it.

At the time, compile definitions from linked targets were added to the
COMPILE_DEFINITIONS property by target_link_libraries. The way such
transitive compile definitions worked was changed in subsequent
commit a1c4905f (Use the link information as a source of compile
definitions and includes., 2013-02-12), so that the COMPILE_DEFINITIONS
property may be empty, despite the fact that there are definitions
which should be used.

Source/cmQtAutomoc.cxx

@@ -280,13 +280,9 @@ void cmQtAutomoc::SetupAutomocTarget(cmTarget* target)
     _moc_incs += *incDirIt;
     }
 
-  const char* tmp = target->GetProperty("COMPILE_DEFINITIONS");
-  std::string _moc_compile_defs;
-  if (tmp)
-    {
-    _moc_compile_defs = target->GetCompileDefinitions(0);
-    }
-  tmp = makefile->GetProperty("COMPILE_DEFINITIONS");
+  std::string _moc_compile_defs = target->GetCompileDefinitions(0);
+
+  const char* tmp = makefile->GetProperty("COMPILE_DEFINITIONS");
   if (tmp)
     {
     _moc_compile_defs += ";";