Specify the fully qualified class name of the LibGraalClassLoader implementation that gets used for building libgraal.

This option is only supported for building the libgraal shared library.
The given fully qualified class name has to be a subtype of
jdk.graal.compiler.hotspot.libgraal.LibGraalClassLoaderBase.

When building the libgraal shared library, this option is used to specify a custom loader
the builder instantiates via default constructor, that affects image building as follows:

 1. The custom loader is used to lookup Feature implementations passed via the --features option.
 2. All @CEntryPoint definitions from classes managed by the custom loader are processed.
 3. All @TargetClass substitutions in classes managed by the custom loader are processed.
