RISC-V: Moved syscalls to separate files to fix aliasing problems.

libgloss/riscv/sys_openat.c

@@ -0,0 +1,8 @@
+#include <machine/syscall.h>
+#include "internal_syscall.h"
+
+/* Open file relative to given directory.  */
+int _openat(int dirfd, const char *name, int flags, int mode)
+{
+  return syscall_errno (SYS_openat, dirfd, name, flags, mode, 0, 0);
+}