C++: Suppress PointlessSelfComparison on templates

It's a bit crude to suppress all results in instantiations, but we're
already using this kind of suppression in `PointlessComparison.ql`
(without the `Self`) because there is no convenient alternative. It
means we lose some good results but also suppress a new false positive
in Boost that surfaced after we added support for non-type template
parameters.

Author: jbj

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

@@ -19,6 +19,7 @@ where
   pointlessSelfComparison(cmp) and
   not nanTest(cmp) and
   not overflowTest(cmp) and
+  not cmp.isFromTemplateInstantiation(_) and
   not exists(MacroInvocation mi |
     // cmp is in mi
     mi.getAnExpandedElement() = cmp and

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/BadAdditionOverflowCheck/PointlessSelfComparison.expected

@@ -1,9 +1,4 @@
-| templates.cpp:20:5:20:25 | ... < ... | Self comparison. |
-| templates.cpp:21:5:21:25 | ... < ... | Self comparison. |
-| templates.cpp:21:5:21:25 | ... < ... | Self comparison. |
-| templates.cpp:22:5:22:25 | ... < ... | Self comparison. |
-| templates.cpp:22:5:22:25 | ... < ... | Self comparison. |
-| templates.cpp:22:5:22:25 | ... < ... | Self comparison. |
+| templates.cpp:17:5:17:25 | ... < ... | Self comparison. |
 | test.cpp:13:11:13:21 | ... == ... | Self comparison. |
 | test.cpp:79:11:79:32 | ... == ... | Self comparison. |
 | test.cpp:83:10:83:15 | ... == ... | Self comparison. |

cpp/ql/test/query-tests/Likely Bugs/Arithmetic/BadAdditionOverflowCheck/templates.cpp

@@ -12,8 +12,8 @@ bool compareValues() {
   // all instantiations in the program, there could still be more such
   // instantiations outside.
   return
-    T1::value < T2::value || // GOOD [FALSE POSITIVE]
-    T1::value < T1::value || // BAD
+    T1::value < T2::value || // GOOD
+    T1::value < T1::value || // BAD [NOT DETECTED]
     C1::value < C1::value ; // BAD
 }