update fmt 12.0.0 -> 12.1.0 (#828)

- Update vendored fmt library from 12.0.0 to 12.1.0
- Disable warnings-as-errors for the fmt build target (third-party code)

## Notable changes in fmt 12.1.0
- **Performance**: Optimized `buffer::append`, resulting in up to ~16% improvement on spdlog benchmarks
- **Bug fixes**:
  - Worked around ABI incompatibility in `std::locale_ref` between clang and gcc
  - Fixed compilation with clang 21 and `-std=c++20`
  - Fixed compilation with locales disabled in header-only mode
  - Fixed dynamic linking issue with clang-cl
  - Fixed compatibility with clang as host compiler for NVCC
- **Formatter improvements**:
  - `std::variant` and `std::expected` formatters now work with `format_as`
  - Added cv-qualified type support to `std::optional` formatter
  - Added demangling support for libc++ and clang-cl
- **C++ modules**: Fixed several compatibility issues, exported `is_compiled_string` and `operator""_cf`
- **Other**: Switched to global `malloc`/`free` to enable allocator customization, made `FMT_USE_CONSTEVAL` user-configurable

1 files changed, 1 insertions, 0 deletions

diff --git a/thirdparty/xmake.lua b/thirdparty/xmake.lua
index f929656a6..1fb5acad7 100644
--- a/thirdparty/xmake.lua
+++ b/thirdparty/xmake.lua
@@ -134,6 +134,7 @@ target("robin-map")
 target("fmt")
     set_kind("static")
     set_group("thirdparty")
+    set_warnings("allextra")
     add_files("fmt/src/format.cc", "fmt/src/os.cc")
     add_headerfiles("fmt/include/**.h")
     add_includedirs("fmt/include", {public=true})