Disable build with gcc < 4.9

Connector uses std::regex to some extent. The support of std::regex comes with gcc version 4.9. With version 4.8 connector can be compiled but is not usable, as first use of regex leads to program termination.

Thus cmake script should be changed to exit with descriptive error, if detected gcc version is <4.9

Seemingly, sles12 and centos7 has gcc 4.8 as a default toolchain, an to build on those platforms apparently gcc upgrade is required