Semihosting syscall reorg: * Split out semihosting/syscalls.c with common implementations. * Reorg arm-compat-semi.c to use syscalls.c. * Minor prep cleanups to m68k, mips, nios2.
Semihosting syscall reorg: * Split out semihosting/syscalls.c with common implementations. * Reorg arm-compat-semi.c to use syscalls.c. * Minor prep cleanups to m68k, mips, nios2.