feature/#487_Use_only_the_newest_compilers_for_standard_pipeline into master
closes #487
From now on standard pipelines compile phx with clang, gcc7.3.1 and msvc. Nightlies are compiled as before (+gcc5.3.1, +gcc6.3.1).
closes #487
From now on standard pipelines compile phx with clang, gcc7.3.1 and msvc. Nightlies are compiled as before (+gcc5.3.1, +gcc6.3.1).