For Travis CI - use Release build configuration when build on bad VM.
Now this rule is applicable for all target platforms (Linux, Windows, Android, and Raspberry-Pi) which have their CI builds run on Linux/Ubuntu host VM. Mac OSX and iOS CI builds are not affected by this rule since they run on OSX host VM which is not susceptible to "bad VM" issue. The idea is to reduce memory consumption during the linking phase and thus avoiding the process being killed due to insufficient memory in the VM.