Fix the following build failure without a C++ compiler:
CMake Error at CMakeLists.txt:24 (project):
No CMAKE_CXX_COMPILER could be found.
Tell CMake where to find the compiler by setting either the environment
variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
to the compiler, or to the compiler name if it is in the PATH.
Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
