[CMake] FindQt4.cmake broken without C language

[Hendrik Sattler]

Hi,

the following case does not work:
$ cat CMakeLists.txt
project(foo CXX)
find_package(Qt4)
$ cmake .
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Looking for Q_WS_X11
CMake Error: Unknown extension ".c" for 
file "/home/hendrik/test/CMakeFiles/CMakeTmp/CheckSymbolExists.c".  
TRY_COMPILE only works for enabled languages.
Currently enabled languages are: CXX
See PROJECT command for help enabling other languages.
-- Looking for Q_WS_X11 - not found.
-- Looking for Q_WS_MAC
CMake Error: Unknown extension ".c" for 
file "/home/hendrik/test/CMakeFiles/CMakeTmp/CheckSymbolExists.c".  
TRY_COMPILE only works for enabled languages.
Currently enabled languages are: CXX
See PROJECT command for help enabling other languages.
-- Looking for Q_WS_MAC - not found.
-- Looking for Q_WS_WIN
CMake Error: Unknown extension ".c" for 
file "/home/hendrik/test/CMakeFiles/CMakeTmp/CheckSymbolExists.c".  
TRY_COMPILE only works for enabled languages.
Currently enabled languages are: CXX
See PROJECT command for help enabling other languages.
-- Looking for Q_WS_WIN - not found.
-- Found Qt-Version 4.2.2
-- Configuring done

HS