Cannot find Carla on Linux

[minijackson]

Hello, and thanks for this amazing piece of software!

Right now, the Carla Plugin Host and Ildaeil modules can't find Carla on my NixOS system, as it is not installed in /usr/local/lib nor /usr/lib.

What do you think about allowing an environment variable to specify the absolute path to Carla's lib directory?

Related code:

• Cardinal/plugins/Cardinal/src/Carla.cpp

  Lines 159 to 168 in d2a504c

  	else if (system::exists("/usr/local/lib/carla"))
  	{
  	binaryDir = "/usr/local/lib/carla";
  	resourceDir = "/usr/local/share/carla/resources";
  	}
  	else if (system::exists("/usr/lib/carla"))
  	{
  	binaryDir = "/usr/lib/carla";
  	resourceDir = "/usr/share/carla/resources";
  	}

• Cardinal/plugins/Cardinal/src/Ildaeil.cpp

  Lines 507 to 518 in d2a504c

  	else if (system::exists("/usr/local/lib/carla"))
  	{
  	fBinaryPath = "/usr/local/lib/carla";
  	carla_set_engine_option(fCarlaHostHandle, ENGINE_OPTION_PATH_BINARIES, 0, "/usr/local/lib/carla");
  	carla_set_engine_option(fCarlaHostHandle, ENGINE_OPTION_PATH_RESOURCES, 0, "/usr/local/share/carla/resources");
  	}
  	else if (system::exists("/usr/lib/carla"))
  	{
  	fBinaryPath = "/usr/lib/carla";
  	carla_set_engine_option(fCarlaHostHandle, ENGINE_OPTION_PATH_BINARIES, 0, "/usr/lib/carla");
  	carla_set_engine_option(fCarlaHostHandle, ENGINE_OPTION_PATH_RESOURCES, 0, "/usr/share/carla/resources");
  	}