[CMake] Disabling C for C++-only projects

[Johannes Zarl]

Hi,

Out of curiosity (and thinking about saving a couple of seconds during the 
first cmake run) I tried just to use C++ as language for some KDE program.

It turns out that without C enabled, standard modules like FindKDE, FindQt4 
and FindJPEG don't run because they use the CheckSymbolExists module.

I'm wondering if this counts as a bug in FindQt4 and FindKDE, because after 
all these two projects are C++, so any platform test should IMO be using the 
same compiler as the build-process does? 

Cheers,
  Johannes