* lib/linux/riscv64-mes-gcc/crt1.c (_start): Replace manual initialization
of __stdin, __stdout, __stderr, and environ with __init_io ().
* lib/linux/riscv64-mes-mescc/crt1.c (_start): Likewise.
* include/linux/syscall.h (_sys_call5): Declare 5-argument syscall needed
for SYS_renameat2, currently only used on RISC-V64.
* lib/linux/riscv64-mes-gcc/syscall.c (__sys_call5, _sys_call5):
Implement it.
* lib/linux/riscv64-mes-gcc/_exit.c,
lib/linux/riscv64-mes-gcc/_write.c,
lib/linux/riscv64-mes-gcc/crt1.c,
lib/linux/riscv64-mes-gcc/syscall-internal.c,
lib/linux/riscv64-mes-gcc/syscall.c: New files to make it possible
to compile mes for riscv64-mes-gcc.
