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 https://github.com/apache/nuttx/issues/14773
on linux.
b4e5c74319