riscv64: Port to word based mescc-tools.
* module/mescc/M1.scm (riscv:i-format, riscv:j-format, riscv:u-format):
New procedures for RISC-V instruction formats.
(info->M1): Use them to switch from !0xAB to M1
weird strings 'AB'.
* module/mescc/riscv64/as.scm,
lib/linux/riscv64-mes-m2/_exit.c
ib/linux/riscv64-mes-m2/_write.c,.
lib/linux/riscv64-mes-m2/crt1.M1,.
lib/linux/riscv64-mes-m2/syscall.c,.
lib/linux/riscv64-mes-mescc/_exit.c,.
lib/linux/riscv64-mes-mescc/_write.c,.
lib/linux/riscv64-mes-mescc/crt1.c,.
lib/linux/riscv64-mes-mescc/syscall-internal.c,.
lib/linux/riscv64-mes-mescc/syscall.c,.
lib/m2/riscv64/riscv64_defs.M1,.
lib/riscv64-mes-mescc/setjmp.c,.
lib/riscv64-mes/riscv64.M1: Switch to riscv64 word-based macros.
* lib/linux/open.c (open)[!SYS_open]: Add support using openat syscall.
* include/linux/riscv64/syscall.h (MAKESTRING, MAKESTRING2,
RISCV_SYSCALL): New macros.
16f4fc3263