* 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.
* 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: New files. These add support for
building for riscv64-mes-mescc and make it self-hosting.
