GXemul Code2

SGI boot / partition work-in-progress.

Some minor refactoring of arcbios environment variables etc, to attempt to get emulated O2 boot-from-disk image (or cdrom image) to work better.

The ECOFF file loader can now (barely) load relocated binaries, such as "sash" from an IRIX installation on my real O2.

One -v on the command line should be enough to see file loading details.

Enabling -Werror again; seems to work on my machine for clang and most GNU C++ versions (up to 9).

bootblock.cc now parses SGI disk boot blocks, and tries to load the OSLoader (sash), if booting without an explicitly provided OS kernel.

Slightly nicer indentation for ARC/ARCS boot info.

Reshuffling the TODO.

Adding support for masks for memory mapped components in the new framework. Used so far by the HP 700/RX, which has 2 MB RAM repeated throughout 0x30000000..0x3fffffff.

Message when trying to disassemble too far.