build (cmake): ZMQ_BUILD_FRAMEWORK causes configure errors

[fanquake]

Issue description

Passing -DZMQ_BUILD_FRAMEWORK=ON to Cmake causes errors.

Environment

• libzmq version (commit hash if unreleased): ee29bcd
• OS: macOS

Minimal test code / Steps to reproduce the issue

1. cmake -B build -DZMQ_BUILD_FRAMEWORK=ON

What's the actual result?

CMake Error at CMakeLists.txt:1294 (add_custom_command):
  No TARGET 'libzmq' has been created in this directory.
....
-- Configuring incomplete, errors occurred!

What's the expected result?

No errors.