[tests] prepare test for reparsing C output

tests/basic/printer.cpp

+/* run.config
+NOFRAMAC:
+EXECNOW: LOG printer.res.c @frama-c@ @PTEST_FILE@ @CXX@ @MACHDEP@ -cxx-keep-mangling -ocode printer.res.c -print
+EXECNOW: @frama-c@ @CXX@ @MACHDEP@ -cxx-demangling-short printer.res.c -print
+*/
+
+namespace A {
+  struct B {
+    int x;
+    B() { x = 42; }
+  };
+}; // namespace A
+
+int main() {
+  A::B b;
+  return b.x;
+}