Provides workarounds for two problems encountered with
crates for plugin-style shared libraries, where the library refers
to symbols in the host program:
- Linking errors on some platforms due to undefined symbols
- Difficulty finding the produced shared library for testing or installation
call from build.rs to emit build flags for building a plugin-style cdylib
return the absolute path of the generated cdylib, using the CARGO_PKG_NAME environment variable and the current directory.