Enable static linking without specifying link dirs

[drahnr]

Use .statik(std::env::var("OPENSSL_STATIC").is_ok()) in fn try_pkg_config() which would remove the need to specify the _INCLUDE_DIR and _LIB_DIR for the case like fedora where the statically linked binaries are provided in the standard locations beside the dynamically linked.

[sfackler]

pkg-config-rs already looks at that environment variable. You're probably running into rust-lang/pkg-config-rs#37

[drahnr]

You are right, this ticket is misplaced.

Just for reference, there is this rust lang forum topic: https://users.rust-lang.org/t/how-to-link-openssl-statically/14912/2 and ticket rust-lang/pkg-config-rs#54 for pkg-config-rs