libcue: fix build without C++

libcue: fix build without C++

By default, CMake assumes that the project is using both C and C++. By
explicitly passing 'C' as argument of the project() macro, we tell
CMake that only C is used, which prevents CMake from checking if a C++
compiler exists.
Patch sent upstream: https://github.com/lipnitsk/libcue/pull/17

Fixes:
 - http://autobuild.buildroot.net/results/a5344d18dbdc86705853fbf8a66d5304de07a9b2

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