C++: Suppress pointless compare in template inst.

It still runs on uninstantiated templates because its underlying
libraries do. It's not clear whether that leads to other false
positives, but that's independent of the change I'm making here.

cpp/ql/src/Likely Bugs/Arithmetic/PointlessComparison.ql

@@ -22,13 +22,15 @@ import UnsignedGEZero
 // #define PRINTMSG(val,msg) { if (val >= PRINTLEVEL) printf(msg); }
 //
 // So to reduce the number of false positives, we do not report a result if
-// the comparison is in a macro expansion.
+// the comparison is in a macro expansion. Similarly for template
+// instantiations.
 from
   ComparisonOperation cmp, SmallSide ss,
   float left, float right, boolean value,
   string reason
 where
   not cmp.isInMacroExpansion() and
+  not cmp.isFromTemplateInstantiation(_) and
   reachablePointlessComparison(cmp, left, right, value, ss) and
 
   // a comparison between an enum and zero is always valid because whether