package/waffle: fix build without C++

Drop C++ dependency as nacl is disabled (and will be dropped by upstream
in next release) to avoid the following build failure raised since bump
to version 1.6.1 in commit 814f36fd:

CMake Error at /usr/share/cmake-3.22/Modules/CMakeTestCXXCompiler.cmake:62 (message):
  The C++ compiler

    "/usr/bin/clang++"

  is not able to compile a simple test program.

Fixes:
 - http://autobuild.buildroot.org/results/a702495074b0393682c619781c349ce62e123133



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>