capnp fails when cross-compiling #28993
Description
On the master branch @ 160d236, the native/bin/capnp fails when cross-compiling with MULTIPROCESS=1:
GEN /home/hebasto/git/bitcoin/depends/x86_64-pc-linux-gnu/include/mp/proxy.capnp.h
/home/hebasto/git/bitcoin/depends/x86_64-pc-linux-gnu/include/mp/proxy.capnp: File is not in the current directory and does not match any prefix defined with --src-prefix. Please pass an appropriate --src-prefix so I can figure out where to write the output for this file.
/home/hebasto/git/bitcoin/depends/x86_64-apple-darwin/native/bin/capnp compile: /home/hebasto/git/bitcoin/depends/x86_64-pc-linux-gnu/include/mp/proxy.capnp: no such file
Try '/home/hebasto/git/bitcoin/depends/x86_64-apple-darwin/native/bin/capnp compile --help' for more information.
terminate called after throwing an instance of 'std::runtime_error'
what(): Invoking /home/hebasto/git/bitcoin/depends/x86_64-apple-darwin/native/bin/capnp failed
make[2]: *** [/home/hebasto/git/bitcoin/depends/x86_64-apple-darwin/native/include/mpgen.mk:4: /home/hebasto/git/bitcoin/depends/x86_64-pc-linux-gnu/include/mp/proxy.capnp.h] Aborted (core dumped)
Please note, that it looks for x86_64-pc-linux-gnu subdirectory, while HOST=x86_64-apple-darwin.
UPDATE: The bug happens on Ubuntu 23.10, but not on Ubuntu 22.04.