[libc++] Check _LIBCPP_USE_CLOCK_GETTIME before using clock_gettime

[ldionne]

Summary

[libc++] Check _LIBCPP_USE_CLOCK_GETTIME before using clock_gettime

The clock_gettime function is available when _POSIX_TIMERS is defined.
We check for this and set _LIBCPP_USE_CLOCK_GETTIME accordingly since
59b3102739c. But check for _LIBCPP_USE_CLOCK_GETTIME was removed in
babd3aefc91. As a result, code is now trying to use clock_gettime even
on platform where it is not available and it is causing build failure with newlib

This patch restores the checks to fix this.

[ldionne]

We don't have CI on newlib. Would you be willing to set some up so we can officially support that configuration?

Commandeering to apply a slightly different fix.

[ldionne]

Simplify the logic for #include

[ldionne]

Update commit author

[abidh]

In D88825#2312905, @ldionne wrote:

Thanks for the review.

We don't have CI on newlib. Would you be willing to set some up so we can officially support that configuration?

I would like to setup the CI as I have more patches coming up that improve newlib support. Do we have any guidance/documentation on how to setup a CI?

Commandeering to apply a slightly different fix.

The updated patch looks ok to me.

[ldionne]

In D88825#2313861, @abidh wrote:

In D88825#2312905, @ldionne wrote:

Thanks for the review.

We don't have CI on newlib. Would you be willing to set some up so we can officially support that configuration?

I would like to setup the CI as I have more patches coming up that improve newlib support. Do we have any guidance/documentation on how to setup a CI?

I need to write some. I'll do that and ping you.

libcxx/src/chrono.cpp

 //===------------------------- chrono.cpp ---------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "chrono"
 #include "cerrno"        // errno
 #include "system_error"  // __throw_system_error
 #include <time.h>        // clock_gettime and CLOCK_{MONOTONIC,REALTIME,MONOTONIC_RAW}
 #include "include/apple_availability.h"
 
 #if __has_include(<unistd.h>)
-#include <unistd.h>
+# include <unistd.h>
 #endif
 
+#if __has_include(<sys/time.h>)
+# include <sys/time.h> // for gettimeofday and timeval
+#endif
+
 #if !defined(__APPLE__) && _POSIX_TIMERS > 0
-#define _LIBCPP_USE_CLOCK_GETTIME
+# define _LIBCPP_USE_CLOCK_GETTIME
 #endif
 
 #if defined(_LIBCPP_WIN32API)
 #  define WIN32_LEAN_AND_MEAN
 #  define VC_EXTRA_LEAN
 #  include <windows.h>
 #  if _WIN32_WINNT >= _WIN32_WINNT_WIN8
 #    include <winapifamily.h>
 #  endif
-#else
-#  if !defined(CLOCK_REALTIME)
-#    include <sys/time.h>        // for gettimeofday and timeval
-#  endif // !defined(CLOCK_REALTIME)
 #endif // defined(_LIBCPP_WIN32API)
 
 #if defined(__ELF__) && defined(_LIBCPP_LINK_RT_LIB)
 #  pragma comment(lib, "rt")
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 

 #else
   GetSystemTimeAsFileTime(&ft);
 #endif
 
   filetime_duration d{(static_cast<__int64>(ft.dwHighDateTime) << 32) |
                        static_cast<__int64>(ft.dwLowDateTime)};
   return time_point(duration_cast<duration>(d - nt_to_unix_epoch));
 #else
-#if defined(CLOCK_REALTIME)
+#if defined(CLOCK_REALTIME) && defined(_LIBCPP_USE_CLOCK_GETTIME)
   struct timespec tp;
   if (0 != clock_gettime(CLOCK_REALTIME, &tp))
     __throw_system_error(errno, "clock_gettime(CLOCK_REALTIME) failed");
   return time_point(seconds(tp.tv_sec) + microseconds(tp.tv_nsec / 1000));
 #else
     timeval tv;
     gettimeofday(&tv, 0);
     return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
-#endif // CLOCK_REALTIME
+#endif
 #endif
 }
 
 time_t
 system_clock::to_time_t(const time_point& t) _NOEXCEPT
 {
     return time_t(duration_cast<seconds>(t.time_since_epoch()).count());
 }