Remove zero-length array of brand dependencies from generated headers when there are none.

Zero-length arrays are a GNU extension.
Update bootstraps.
Fix missing field `brand` in `ResolvedDecl` initialisers (-Wmissing-field-initializers).
CMake: Turn off warnings for uses of the now-deprecated getDependency() in tests (4692a66).
Remove unused `FIELD_SIZE_NAMES`.
"Move" schema code generation macros into the schema compiler itself.

This removes all instances of the zero-length brand dependencies arrays (04a9c84).
Merge branch 'brandDeps' of github.com:pqu/capnproto into pqu-brandDeps

Conflicts:
	c++/src/capnp/rpc-twoparty.capnp.c++
	c++/src/capnp/rpc-twoparty.capnp.h
	c++/src/capnp/rpc.capnp.c++
	c++/src/capnp/rpc.capnp.h