std: in fmt, use tag names of non-exhaustive enums when available

[daurnimator]

Possible since #4559

[andrewrk]

test case plz

[daurnimator]

Test is failing with:

/Users/runner/runners/2.165.2/work/1/s/lib/std/fmt.zig:381:37: error: evaluation exceeded 1000 backwards branches
                comptime std.mem.eql(u8, fmt, "b"))
                                    ^
/Users/runner/runners/2.165.2/work/1/s/lib/std/fmt.zig:182:35: note: called from here
                    try formatType(
                                  ^
/Users/runner/runners/2.165.2/work/1/s/lib/std/io/out_stream.zig:28:34: note: called from here
            return std.fmt.format(self, format, args);
                                 ^
/Users/runner/runners/2.165.2/work/1/s/lib/std/debug.zig:270:37: note: called from here
                noasync stderr.print(format ++ "\n", args) catch os.abort();
                                    ^
/Users/runner/runners/2.165.2/work/1/s/lib/std/debug.zig:235:15: note: called from here
    panicExtra(null, first_trace_addr, format, args);
              ^
/Users/runner/runners/2.165.2/work/1/s/lib/std/os/windows.zig:407:36: note: called from here
                    std.debug.panic("unexpected error: {}\n", .{err});
                                   ^
/Users/runner/runners/2.165.2/work/1/s/lib/std/os/windows.zig:393:35: note: called from here
) GetQueuedCompletionStatusResult {
                                  ^

I suspect because of iterating over a large enum with

                inline for (enumInfo.fields) |enumField| {
                    if (@enumToInt(value) == enumField.value) {
                        has_name = true;
                        break;
                    }
                }

Should I put in a @setEvalBranchQuota? or what is the recommended solution?