Add an SD node for turning a stack-pointer-relative address into a stack-capability-relative address.
Add some missing enum to string conversions (useful for debugging only).
Add a calling convention for variadic functions in the sandbox ABI.  This passes everything on the stack.  This ends up being more efficient than the normal MIPS calling convention for functions with few non-variadic functions, because the callee is required to spill all 8 integer argument registers to the stack on va_start() in the MIPS convention.  The ideal thing would be to pass the variadic arguments on the stack and non-variadic arguments in registers.
Use the new variadic calling convention.