Improve POSIX API detection

test/format-test.cc

@@ -1819,7 +1819,7 @@ TEST(FormatIntTest, FormatInt) {
 }
 
 TEST(FormatTest, Print) {
-#if FMT_USE_FILE_DESCRIPTORS
+#if FMT_USE_FCNTL
   EXPECT_WRITE(stdout, fmt::print("Don't {}!", "panic"), "Don't panic!");
   EXPECT_WRITE(stderr, fmt::print(stderr, "Don't {}!", "panic"),
                "Don't panic!");