Fix CMake variable for regex availability check.
Fix CMake variable for regex availability check.

saschazelzer/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,CppMicroServices/CppMicroServices,saschazelzer/CppMicroServices