This breaks builds of libc with top of tree clang under -Werror.

This pr is to resovle #126948

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Co-authored-by: Joseph Huber <huberjn@outlook.com>

In the process of adding strftime (#122556) I wrote this utility class
to simplify reading from a struct tm. It provides helper functions that
return basically everything needed by strftime. It's not tested
directly, but it is thoroughly exercised by the strftime tests.

While working on strftime I noticed some constants were being defined in
unexpected places. One thing led to another, and I ended up doing a
major cleanup of the time functions.

What's included:
All uses of <time.h> in /src and /test removed (except for LibcTest.cpp)
The various time constants have been moved to time_constants.h, and the
`time_constants` namespace.
struct tm gets its own type indirection header now.

This is a part of #97655.

Reverts llvm/llvm-project#98075

bots are broken

This is a part of #97655.

This is step 4 of
https://discourse.llvm.org/t/rfc-customizable-namespace-to-allow-testing-the-libc-when-the-system-libc-is-also-llvms-libc/73079

This patch fixes the overflow check in update_from_seconds, used by
gmtime, gmtime_r and mktime.

In update_from_seconds, total_seconds is a int64_t and the previous
overflow check for when sizeof(time_t) == 4 would check if it was <
0x80000000 and > 0x7FFFFFFF, however, this check would cause the
following issues:

1. Valid negative numbers would be discarded, e.g., -1 is
0xffffffffffffffff as a int64_t, outside the range of the overflow
check.

2. Some valid positive numbers would be discarded because the hex
constants were being implicitly converted to int64_t, e.g., 0x80000000
would be implicitly converted to 2147483648, instead of -2147483648.

The fix for both cases was to static_cast total_seconds and the
constants to time_t if sizeof(time_t) == 4. The behaviour is not changed
in systems with sizeof(time_t) == 8.

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Signed-off-by: Mikhail R. Gadelha <mikhail@igalia.com>