Support setting _NET_WM_PID in X11 environments

Support is added for setting _NET_WM_PID automatically. This is to
support scripting of the window environment. For example, this makes it
possible to script opening a window with same CWD:

1. Retrieve the current window
2. (new) get PID of window
3. Check if it's Alacritty, find first child (presumably a shell), and
   get the child's cwd.
4. Spawn new instance of terminal with cwd.

Unaddressed in this commit is how this will coexist on a Wayland system.

1 files changed, 3 insertions, 0 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 6ea5935c..10e6fbd3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -35,6 +35,9 @@ unicode-width = "0.1.4"
 
 clippy = { version = "0.0.104", optional = true }
 
+[target.'cfg(any(target_os = "linux", target_os = "freebsd", target_os="dragonfly", target_os="openbsd"))'.dependencies]
+x11-dl = "2.12.0"
+
 [features]
 default = ["err-println"]
 # Enabling this feature makes shaders automatically reload when changed