Fix ambigious call to fprintf when compiling as a C++20 module

[tsarn]

Fixes the following error when compiling with Clang and -DFMT_MODULE=ON:

In file included from <fmt>/src/fmt.cc:147:
In file included from <fmt>/src/format.cc:8:
<fmt>/include/fmt/format-inl.h:39:3: error: call to 'fprintf' is ambiguous
   39 |   fprintf(stderr, "%s:%d: assertion failed: %s", file, line, message);
      |   ^~~~~~~
/usr/include/stdio.h:360:12: note: candidate function
  360 | extern int fprintf (FILE *__restrict __stream,
      |            ^
<fmt>/include/fmt/printf.h:599:13: note: candidate function [with T = <const char *, int, const char *>]
  599 | inline auto fprintf(std::FILE* f, string_view fmt, const T&... args) -> int {
      |             ^

Compiling with GCC produces a warning instead

[vitaut]

Thank you!