fix: defer volume lock to after setup, fix sighandler cast comment, check pkg-config status

crates/ahfail-display/build.rs

@@ -37,6 +37,7 @@ fn main() {
         .args(["--cflags", "gio-2.0"])
         .output()
         .expect("pkg-config not found");
+    assert!(gio_cflags.status.success(), "pkg-config --cflags gio-2.0 failed");
     let gio_cflags_str = String::from_utf8(gio_cflags.stdout).unwrap();
 
     let mut build = cc::Build::new();