For some reason, the configure command must be specified explicitly in the `gentables` build step. Otherwise, the ARM target compiler will be used to build `make_tables` rather than the host compiler.
Now that microsoft/vcpkg#10485 has been completed, an ARM CI build can be added to AppVeyor. Also, the build status table in the README has been updated.
* cleanup unneeded compiler variations (now builds in 7 min rather than 13 min)
* Windows:
* use VS2017 for vcpkg, VS2015 for manual build
* Linux:
* install alsa, jack, pulse, portaudio, ladspa, libsndfile for all builds
* MacOSX:
* use AppleClang
* reorder macosx build in between linux build, as macosx usually takes longer to build, allowing to make better use of build time (via pipelining)
* switch to XCode10, enabling TravisCI to support CoreAudio and CoreMidi
