Fix visibility in Rust linkage
- Allow bindgen visibility override in order to be able to see some pattern manipulation functions that are needed on the Rust side. The BINDGEN_IGNORE_VISIBILITY is only to be set by the bindgen invocation.
- Move the closure of functions for pattern manipulation and their dependencies into a buildtime-temporary static library which is then immediately linked into the fontconfig library. This makes the internal symbols visible to Rust testing.
- Hide Rust library symbols in the externally visible Fontconfig
library. Without the
-Wl,--exclude-libs,libfc_fontations
link args Rust library symbols would appear as externally visible.
Fixes #441.