Auto merge of #18877 - emilio:closest-why, r=nox

stylo: Dumb down the return value of SelectorList_Closest.

So it builds with rust 1.21.

See: https://bugzilla.mozilla.org/show_bug.cgi?id=1408622

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components/style/gecko/generated/bindings.rs

@@ -1921,6 +1921,11 @@ extern "C" {
     pub fn Gecko_AddBufferToCrashReport(addr: *const ::std::os::raw::c_void,
                                         len: usize);
 }
+extern "C" {
+    pub fn Gecko_AnnotateCrashReport(key_str: *const ::std::os::raw::c_char,
+                                     value_str:
+                                         *const ::std::os::raw::c_char);
+}
 extern "C" {
     pub fn Servo_Element_ClearData(node: RawGeckoElementBorrowed);
 }
@@ -2118,6 +2123,11 @@ extern "C" {
                                       arg2: RawServoSelectorListBorrowed)
      -> bool;
 }
+extern "C" {
+    pub fn Servo_SelectorList_Closest(arg1: RawGeckoElementBorrowed,
+                                      arg2: RawServoSelectorListBorrowed)
+     -> *const RawGeckoElement;
+}
 extern "C" {
     pub fn Servo_StyleSet_AddSizeOfExcludingThis(malloc_size_of: MallocSizeOf,
                                                  malloc_enclosing_size_of: