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

libgloss/riscv/sys_execve.c

@@ -0,0 +1,11 @@
+#include <machine/syscall.h>
+#include "internal_syscall.h"
+
+/* Transfer control to a new process. Minimal implementation for a
+   system without processes from newlib documentation.  */
+int
+_execve(const char *name, char *const argv[], char *const env[])
+{
+  errno = ENOMEM;
+  return -1;
+}