C++: Add upgrade and downgrade scripts

cpp/downgrades/801b2f03360d78c85f51fbad9b75956fa8d58b00/functions.ql

@@ -0,0 +1,9 @@
+class Function extends @function {
+  string toString() { none() }
+}
+
+from Function f, string n, int k, int new_k
+where
+  functions(f, n, k) and
+  if builtin_functions(f) then new_k = 6 else new_k = k
+select f, n, new_k

cpp/downgrades/801b2f03360d78c85f51fbad9b75956fa8d58b00/upgrade.properties

@@ -0,0 +1,4 @@
+description: Move builtin function identification to its own table
+compatibility: full
+functions.rel: run functions.qlo
+builtin_functions.rel: delete

cpp/ql/lib/upgrades/5491582ac8511726e12fae3e2399000f9201cd9a/builtin_functions.ql

@@ -0,0 +1,7 @@
+class Function extends @function {
+  string toString() { none() }
+}
+
+from Function f
+where functions(f, _, 6)
+select f

cpp/ql/lib/upgrades/5491582ac8511726e12fae3e2399000f9201cd9a/functions.ql

@@ -0,0 +1,9 @@
+class Function extends @function {
+  string toString() { none() }
+}
+
+from Function f, string n, int k, int new_k
+where
+  functions(f, n, k) and
+  if k = 6 then new_k = 1 else new_k = k
+select f, n, new_k

cpp/ql/lib/upgrades/5491582ac8511726e12fae3e2399000f9201cd9a/upgrade.properties

@@ -0,0 +1,4 @@
+description: Move builtin function identification to its own table
+compatibility: full
+functions.rel: run functions.qlo
+builtin_functions.rel: run builtin_functions.qlo