[Firestore] Add unlinked symbol introduced in #12370

Author: ncooke3

Firestore/Source/API/FIRFirestore.mm

@@ -567,12 +567,14 @@ - (void)terminateInternalWithCompletion:(nullable void (^)(NSError *_Nullable er
 #pragma mark - Force Link Unreferenced Symbols
 
 extern void FSTIncludeFSTFirestoreComponent(void);
+extern void FSTIncludeFIRSnapshotListenOptions(void);
 
 /// This method forces the linker to include all the Analytics categories without requiring app
 /// developers to include the '-ObjC' linker flag in their projects. DO NOT CALL THIS METHOD.
 + (void)notCalled {
   NSAssert(NO, @"+notCalled should never be called");
   FSTIncludeFSTFirestoreComponent();
+  FSTIncludeFIRSnapshotListenOptions();
 }
 
 @end

Firestore/Source/API/FIRSnapshotListenOptions.mm

@@ -58,6 +58,11 @@ - (FIRSnapshotListenOptions *)optionsWithSource:(FIRListenSource)source {
   return newOptions;
 }
 
+/// This function forces the linker to include `FIRSnapshotListenOptions`.
+/// See `+[FIRFirestore notCalled]`.
+void FSTIncludeFIRSnapshotListenOptions(void) {
+}
+
 @end
 
 NS_ASSUME_NONNULL_END