arch/sim/src/nuttx-names.in: Add pipe2

This breaks the libuv build without CONFIG_PIPES
as expected:

```
LD:  nuttx
/usr/bin/ld: nuttx.rel: in function `uv_pipe':
/src/apps/system/libuv/libuv/src/unix/pipe.c:516: undefined reference to `NXpipe2'
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:427: nuttx] Error 1
make: *** [tools/Unix.mk:551: nuttx] Error 2
```

That is, this correctly exposes #14773
on linux.

arch/sim/src/nuttx-names.in

@@ -90,6 +90,7 @@ NXSYMBOLS(munmap)
 NXSYMBOLS(open)
 NXSYMBOLS(opendir)
 NXSYMBOLS(pclose)
+NXSYMBOLS(pipe2)
 NXSYMBOLS(perror)
 NXSYMBOLS(poll)
 NXSYMBOLS(popen)