app: Enable building on OpenBSD

Currently the golang.org/x/sys package is missing the Pipe2 call for OpenBSD.
The call exists on OpenBSD, it just isn't exposed.

This diff was tested buy adding the Pipe2 call and setting:

   go mod edit -replace=golang.org/x/sys=/pat/to/modified/sys

Signed-off-by: Aaron Bieber <aaron@bolddaemon.com>

app/internal/xkb/xkb_unix.go

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: Unlicense OR MIT
 
-// +build linux,!android freebsd
+// +build linux,!android freebsd openbsd
 
 // Package xkb implements a Go interface for the X Keyboard Extension library.
 package xkb
@@ -20,8 +20,8 @@ import (
 
 /*
 #cgo LDFLAGS: -lxkbcommon
-#cgo freebsd CFLAGS: -I/usr/local/include
-#cgo freebsd LDFLAGS: -L/usr/local/lib
+#cgo freebsd openbsd CFLAGS: -I/usr/local/include
+#cgo freebsd openbsd LDFLAGS: -L/usr/local/lib
 
 #include <stdlib.h>
 #include <xkbcommon/xkbcommon.h>