UserspaceEmulator: Add the dup2 syscall

DevTools/UserspaceEmulator/Emulator.cpp

@@ -253,6 +253,8 @@ u32 Emulator::virt_syscall(u32 function, u32 arg1, u32 arg2, u32 arg3)
     switch (function) {
     case SC_chdir:
         return virt$chdir(arg1, arg2);
+    case SC_dup2:
+        return virt$dup2(arg1, arg2);
     case SC_access:
         return virt$access(arg1, arg2, arg3);
     case SC_waitid:
@@ -1346,4 +1348,9 @@ int Emulator::virt$chdir(FlatPtr path, size_t path_length)
     return syscall(SC_chdir, host_path.data(), host_path.size());
 }
 
+int Emulator::virt$dup2(int old_fd, int new_fd)
+{
+    return syscall(SC_dup2, old_fd, new_fd);
+}
+
 }

DevTools/UserspaceEmulator/Emulator.h

@@ -138,6 +138,7 @@ private:
     ssize_t virt$getrandom(FlatPtr buffer, size_t buffer_size, unsigned int flags);
     int virt$sleep(unsigned);
     int virt$chdir(FlatPtr, size_t);
+    int virt$dup2(int, int);
     int virt$getpgrp();
     int virt$getpgid(pid_t);
     int virt$setpgid(pid_t pid, pid_t pgid);