Ninja: Fix detection of custom command symbolic outputs

Fix logic introduced by commit v3.5.0-rc1~198^2 (Ninja: Always re-run
custom commands that have symbolic dependencies, 2015-11-19) to not
consider only the last output.  We need to know if any output is
SYMBOLIC, so stop checking as soon as one is found.

Source/cmLocalNinjaGenerator.cxx

@@ -400,7 +400,7 @@ cmLocalNinjaGenerator::WriteCustomCommandBuildStatement(
 
   bool symbolic = false;
   for (std::vector<std::string>::const_iterator o = outputs.begin();
-       o != outputs.end(); ++o)
+       !symbolic && o != outputs.end(); ++o)
     {
     if (cmSourceFile* sf = this->Makefile->GetSource(*o))
       {