Fix tests compilation

* CPlusPlusForwardDeclarations.h not found
* Valgrind tests that include botan missing -ldl.
  botan is not required for them (they link just fine without it).

Change-Id: I279b03990ad36d01c93700d50ae8e5119bf5be80
Reviewed-by: André Hartmann <aha_1980@gmx.de>
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@digia.com>