More explicit warning when C++ compiler not used for C++ Cython file.
More explicit warning when C++ compiler not used for C++ Cython file.

Now that we split CInitCode and CppInitCode, we no longer generate
valid C code even if C++ features are not used.

mrGeen/cython,scoder/cython,ChristopherHogan/cython,roxyboy/cython,mcanthony/cython,roxyboy/cython,da-woods/cython,encukou/cython,mrGeen/cython,JelleZijlstra/cython,encukou/cython,fabianrost84/cython,mrGeen/cython,scoder/cython,dahebolangkuan/cython,mcanthony/cython,da-woods/cython,JelleZijlstra/cython,c-blake/cython,scoder/cython,roxyboy/cython,fabianrost84/cython,madjar/cython,mrGeen/cython,cython/cython,da-woods/cython,fabianrost84/cython,achernet/cython,acrispin/cython,slonik-az/cython,acrispin/cython,mcanthony/cython,fperez/cython,scoder/cython,achernet/cython,madjar/cython,achernet/cython,hickford/cython,hickford/cython,cython/cython,dahebolangkuan/cython,c-blake/cython,madjar/cython,JelleZijlstra/cython,fperez/cython,encukou/cython,cython/cython,achernet/cython,hhsprings/cython,roxyboy/cython,acrispin/cython,fperez/cython,dahebolangkuan/cython,hickford/cython,c-blake/cython,JelleZijlstra/cython,ChristopherHogan/cython,JelleZijlstra/cython,ChristopherHogan/cython,madjar/cython,dahebolangkuan/cython,encukou/cython,c-blake/cython,fabianrost84/cython,fperez/cython,hhsprings/cython,slonik-az/cython,hhsprings/cython,mrGeen/cython,madjar/cython,dahebolangkuan/cython,slonik-az/cython,slonik-az/cython,achernet/cython,hickford/cython,c-blake/cython,cython/cython,da-woods/cython,hhsprings/cython,hhsprings/cython,fabianrost84/cython,mcanthony/cython,hickford/cython,acrispin/cython,mcanthony/cython,fperez/cython,encukou/cython,roxyboy/cython,acrispin/cython,slonik-az/cython