Fix possible infinite recursion in FMT_ASSERT (#1744)

Use std::fprintf for assertion message output preventing infinite
recursion when output to stderr is limited or broken.

include/fmt/format-inl.h

@@ -49,7 +49,9 @@ FMT_BEGIN_NAMESPACE
 namespace detail {
 
 FMT_FUNC void assert_fail(const char* file, int line, const char* message) {
-  print(stderr, "{}:{}: assertion failed: {}", file, line, message);
+  // Use unchecked std::fprintf to avoid triggering another assertion when
+  // writing to stderr fails
+  std::fprintf(stderr, "%s:%d: assertion failed: %s", file, line, message);
   // Chosen instead of std::abort to satisfy Clang in CUDA mode during device
   // code pass.
   std::terminate();