package_ffi requires pkg-config and libffi (find_package(PkgConfig
REQUIRED) + pkg_check_modules(FFI REQUIRED libffi) in
src/packages/ffi/CMakeLists.txt), but the docs, Dockerfile, and CI
package lists never listed them — CI only passed because the runners
preinstall pkg-config.
Add the platform-appropriate packages across every dependency list:
- apt: pkg-config libffi-dev
- brew: libffi (pkg-config already present)
- apk: pkgconf libffi-dev
- pacman: mingw-w64-x86_64-pkgconf mingw-w64-x86_64-libffi
Also note in the build docs that flex is only needed when editing the
LPC lexer; otherwise the pre-committed generated lexer is used.
