C++: Add build mode to the telemetry

cpp/ql/src/Telemetry/Metrics.qll

@@ -266,4 +266,12 @@ module CppMetrics {
 
     override int getValue() { result = count(SyntaxError e) }
   }
+
+  class BuildModeNone extends ExtractionMetric {
+    BuildModeNone() { this = "build mode none" }
+
+    override int getValue() {
+      if exists(Compilation c | c.buildModeNone()) then result = 1 else result = 0
+    }
+  }
 }

cpp/ql/test/library-tests/extraction_errors/ExtractionMetrics.expected

@@ -1,4 +1,5 @@
 | #include directives | 2 |
+| build mode none | 0 |
 | calls | 2 |
 | calls with an explicit target | 1 |
 | compilations | 2 |