Disable non-default features Upstream `lmdb-master-sys` relies on compiling a vendored version of `liblmdb`, providing multiple features enabled using compiler flags and defines. Our Debian package uses the pre-built packaged library, and therefore cannot provide those features. As no consumer of `lmdb-master-sys` currently relies on those features, we can disable them entirely.
Fix the 'bindgen' feature The 'bindgen' feature is used to (re)generate the Rust bindings to the C library. It should not be needed since the bindings are included in the crate anyway, but in case it is, we fix it by generating them from the C headers included in the liblmdb-dev package and saving them to OUT_DIR. Note: the bindings are not generated if we cannot find the system headers in the easiest way possible.
Fix build on Debian Upstream code relies on building a static library from vendored source. For Debian we want to avoid this and would rather use the pre-built, packaged version of `liblmdb`. Using pkg-config is a simple way to ensure the needed linker flags (especially `-llmdb`) are used and the build can therefore succeed.
