[libc++] Avoid <climits> dependency in <thread>

The standard guarantees sleep durations of 2^63-1 nanoseconds to work.
Instead of depending on INT64_MAX or ULONGLONG_MAX to exist via the
header pollution, fold the constant directly. That has the additional
positive side effect that it avoids long double arithmetic bugs in GCC.

Differential Revision: https://reviews.llvm.org/D99516

libcxx/include/thread

@@ -362,12 +362,11 @@ sleep_for(const chrono::duration<_Rep, _Period>& __d)
 {
     if (__d > chrono::duration<_Rep, _Period>::zero())
     {
-#if defined(_LIBCPP_COMPILER_GCC) && (__powerpc__ || __POWERPC__)
-    //  GCC's long double const folding is incomplete for IBM128 long doubles.
-        _LIBCPP_CONSTEXPR chrono::duration<long double> _Max = chrono::duration<long double>(ULLONG_MAX/1000000000ULL) ;
-#else
-        _LIBCPP_CONSTEXPR chrono::duration<long double> _Max = chrono::nanoseconds::max();
-#endif
+        // The standard guarantees a 64bit signed integer resolution for nanoseconds,
+        // so use INT64_MAX / 1e9 as cut-off point. Use a constant to avoid <climits>
+        // and issues with long double folding on PowerPC with GCC.
+        _LIBCPP_CONSTEXPR chrono::duration<long double> _Max =
+            chrono::duration<long double>(9223372036.0L);
         chrono::nanoseconds __ns;
         if (__d < _Max)
         {