C++: Implement compilation_build_mode

cpp/ql/lib/semmle/code/cpp/Compilation.qll

@@ -112,4 +112,7 @@ class Compilation extends @compilation {
    * termination, but crashing due to something like a segfault is not.
    */
   predicate normalTermination() { compilation_finished(this, _, _) }
+
+  /** Holds if this compilation was compiled using the "none" build mode. */
+  predicate buildModeNone() { compilation_build_mode(this, 0) }
 }

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -46,6 +46,20 @@ compilation_args(
     string arg : string ref
 );
 
+/**
+ * Optionally, record the build mode for each compilation.
+ * The build mode should be the same for all compilations.
+ * Build mode:
+ *   0 = none
+ *   1 = manual
+ *   2 = auto
+ */
+#keyset[id, mode]
+compilation_build_mode(
+    int id : @compilation ref,
+    int mode : int ref
+);
+
 /**
  * The source files that are compiled by a compiler invocation.
  * If `id` is for the compiler invocation