cmake: fix broken travis build, which uses cmake 2.8.9
cmake: fix broken travis build, which uses cmake 2.8.9

cmake 2.8.9 doesn't have CMAKE_CXX_COMPILER_VERSION

mejedi/tarantool,KlonD90/tarantool,Sannis/tarantool,condor-the-bird/tarantool,Sannis/tarantool,condor-the-bird/tarantool,KlonD90/tarantool,KlonD90/tarantool,vasilenkomike/tarantool,guard163/tarantool,condor-the-bird/tarantool,ocelot-inc/tarantool,Sannis/tarantool,condor-the-bird/tarantool,ocelot-inc/tarantool,vasilenkomike/tarantool,mejedi/tarantool,guard163/tarantool,vasilenkomike/tarantool,guard163/tarantool,guard163/tarantool,vasilenkomike/tarantool,rtsisyk/tarantool,Sannis/tarantool,KlonD90/tarantool,rtsisyk/tarantool,guard163/tarantool,rtsisyk/tarantool,ocelot-inc/tarantool,KlonD90/tarantool,mejedi/tarantool,condor-the-bird/tarantool,Sannis/tarantool,rtsisyk/tarantool,ocelot-inc/tarantool,vasilenkomike/tarantool,mejedi/tarantool