Fix a build breakage with newer GCC.
Add .gitignore, remove .hgignore.
New cross-compiled toolchain.
Enable -fstack-protector-all.
Generate a bochs.cfg by default.
Fix release-mode.

1. The stack size for kvprintf was potentially too large.
2. The ljmp instruction clobbers memory.
Increase the stack size for the system and mmu drivers.
A slightly more interesting mmu driver (but not too interesting).