build: depends makes libmultiprocess by default

This causes IPC binaries (bitcoin-node, bitcoin-gui) to be included
in releases.

The effect on CI is that this causes more depends builds to build IPC
binaries, but still the only build running functional tests with them
is the i686_multiprocess one.

Except for Windows.

depends/README.md

@@ -96,7 +96,7 @@ The following can be set when running make: `make FOO=bar`
 - `NO_ZMQ`: Don't download/build/cache packages needed for enabling ZeroMQ
 - `NO_WALLET`: Don't download/build/cache libs needed to enable the wallet (SQLite)
 - `NO_USDT`: Don't download/build/cache packages needed for enabling USDT tracepoints
-- `MULTIPROCESS`: Build libmultiprocess (experimental)
+- `NO_IPC`: Don't build Cap’n Proto and libmultiprocess packages. Default on Windows.
 - `DEBUG`: Disable some optimizations and enable more runtime checking
 - `HOST_ID_SALT`: Optional salt to use when generating host package ids
 - `BUILD_ID_SALT`: Optional salt to use when generating build package ids