This is to choose which PALs are to be build and installed. Currently
build happens outside of meson, so this only affects installing and not
building, but if one PAL was not built, then meson would fail because it
won't find the dependency.
Meson is still optional and not needed to build or run anything. It is
needed only to install Graphene in distro.
Currently only a small subset of what is actually needed is installed:
- graphene and graphene-sgx (for now those are slightly massaged copies
of pal_loader),
- libpal.so and sgx loader,
- gdb scripts.
Notably manifests should still point trusted_libs to Runtime/ dir in
repo.
Wojtek Porczyk