fix ambiguous function call

Summary:
# This diff

Qualifies format_to calls with `fmt::` so that the function call is no longer ambiguous

# Context

C++ 20 added std::format_to, which causes bare format_to calls to be ambiguous. We can easily fix the issue by qualifying the calls with `fmt::` as done in this diff.

Reviewed By: narissiam

Differential Revision: D63902777

fbshipit-source-id: ce4c9504f51c8822688829092ef709e7c9ee219b

third-party/watchman/src/watchman/watchman_string.h

@@ -559,7 +559,7 @@ struct formatter<w_string> {
 
   template <typename FormatContext>
   auto format(const w_string& s, FormatContext& ctx) const {
-    return format_to(ctx.out(), "{}", s.view());
+    return fmt::format_to(ctx.out(), "{}", s.view());
   }
 };
 
@@ -572,7 +572,7 @@ struct formatter<w_string_piece> {
 
   template <typename FormatContext>
   auto format(const w_string_piece& s, FormatContext& ctx) const {
-    return format_to(ctx.out(), "{}", s.view());
+    return fmt::format_to(ctx.out(), "{}", s.view());
   }
 };
 } // namespace fmt