Command line option for skipping or passing a custom startup.scd

[sjomae]

When using sclang from the command line in a script, it might be useful to skip the loading of the startup.scd file, if custom / specific instance options are set in the script instead.

Moreover it might be useful to pass a custom startup.scd file from the command line which will load instead of the default startup.scd file.

Disabling and custom startup.scd file, also mentioned here:
#311

These reported enhancement requests could make it more easy to run (multiple) instances of sclang / scsynth from the command line and make them function more like standalone applications or specific SC sessions (Tidal Cycles comes to mind).

#6252 | #6250
#6249

Edit: some code references:

https://github.com/supercollider/supercollider/blob/develop/lang/LangSource/SC_TerminalClient.cpp#L134

supercollider/SCClassLibrary/Platform/Platform.sc

Line 11 in 28a0b12

defaultStartupFile = this.userConfigDir +/+ "startup.scd"

supercollider/SCClassLibrary/Platform/Platform.sc

Line 126 in 28a0b12

loadStartupFiles { this.startupFiles.do{|afile|

https://github.com/supercollider/supercollider/tree/28a0b12216fb97e4487373b2cf00a5ec28850f1f/platform/disable_startup_files