libvlc-sys: declare vsnprintf outside the generated block

vsnprintf is a C-runtime symbol, not a libvlc export, so it has no business
sitting in the block of bindings generated from libvlc's headers. It only
ended up there because the Windows link workaround needed a declaration.

Drop it from the allowlist and declare it by hand in lib.rs.

libvlc-sys/bindings.rs

@@ -1611,12 +1611,6 @@ const _: () = {
         [::core::mem::offset_of!(libvlc_log_message_t, psz_message) - 32usize];
 };
 unsafe extern "C" {
-    pub fn vsnprintf(
-        __s: *mut libc::c_char,
-        __maxlen: libc::c_ulong,
-        __format: *const libc::c_char,
-        __arg: VaList,
-    ) -> libc::c_int;
     pub fn libvlc_errmsg() -> *const libc::c_char;
     pub fn libvlc_clearerr();
     pub fn libvlc_vprinterr(

libvlc-sys/src/lib.rs

@@ -8,3 +8,14 @@ pub mod valist;
 // The bindings are a committed source file, regenerated out of band with
 // `cargo xtask bindgen`.
 include!("../bindings.rs");
+
+// `libc` does not expose vsnprintf and libvlc advises to use it to handle logs in the log
+// callbacks. Expose it for convenience.
+unsafe extern "C" {
+    pub fn vsnprintf(
+        s: *mut libc::c_char,
+        n: usize,
+        fmt: *const libc::c_char,
+        ap: VaList,
+    ) -> libc::c_int;
+}

src/core.rs

@@ -161,7 +161,7 @@ unsafe extern "C" fn logging_cb(
     let f: &Box<dyn Fn(LogLevel, Log, Cow<str>) + Send + 'static> = ::std::mem::transmute(data);
     let mut buf: [c_char; BUF_SIZE] = [0; BUF_SIZE];
 
-    sys::vsnprintf(buf.as_mut_ptr(), BUF_SIZE.try_into().unwrap(), fmt, args);
+    sys::vsnprintf(buf.as_mut_ptr(), BUF_SIZE, fmt, args);
 
     f((level as u32).into(), Log{ptr: ctx}, from_cstr_ref(buf.as_ptr()).unwrap());
 }

xtask/src/main.rs

@@ -43,9 +43,6 @@ fn generate_bindings() {
         .ctypes_prefix("libc")
         // Allowlist every (lib)vlc symbol.
         .allowlist_item("(lib|LIB)?(vlc|VLC)_.*")
-        // Required by the Windows `legacy_stdio_definitions` link workaround
-        // (see libvlc-sys/build.rs).
-        .allowlist_function("vsnprintf")
         // libvlc only uses FILE behind a pointer. Map it
         // to libc's opaque, per-platform FILE rather than emitting glibc's
         // plain _IO_FILE, whose baked-in layout breaks non-Linux builds.