Turns out we can use abi::__cxa_demangle() for this, and all we need to
provide is sprintf(), realloc() and free(), so this patch exposes them.
We now have fully demangled C++ backtraces :^)
serial_debug will output all the kprintf and dbgprintf data to COM1 at
8-N-1 57600 baud. this is particularly useful for debugging the boot
process on live hardware.
Note: it must be the first parameter in the boot cmdline.
Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.
