clang-7.0: build fails in compiler-rt/lib/xray on darwin < 15 due to several issues

[kencu (Ken)]

there are three issues building XRAY on older systems (that I have found so far).

1. It needs thread local storage, which results in systems < darwin 11 failing.
2. MAP_ANONYMOUS is used but undefined on older systems. This is fixed easily enough by replacing the definition with -DMAP_ANONYMOUS=MAP_ANON. I did it by adding the definition in compiler-rt/CMakeLists.txt to cover all the instances at once.
3. error: use of undeclared identifier 'CLOCK_REALTIME'. This one may be harder to fix. There are some example replacement functions <​https://stackoverflow.com/questions/5167269/clock-gettime-alternative-in-mac-os-x> but I'm not sure if any of them truly offer a suitable replacement.

These issues may result in XRAY being disabled on all the non-building systems (currently darwin < 15).

When XRAY is disabled on darwin10 clang-7.0 builds through to completion (this fix is already in the Portfile restricted to darwin 10 or less <​https://github.com/macports/macports-ports/commit/3f03093e264ea484508dbbcc6f8cbc14b18a23df> ).

[kencu (Ken)]

On 10.9:

/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-7.0/clang-7.0/work/llvm-7.0.0rc2.src/projects/compiler-rt/lib/xray/xray_basic_logging.cc:300:32: error: use of undeclared identifier 'CLOCK_REALTIME'
    int result = clock_gettime(CLOCK_REALTIME, &TS);
                               ^
/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_llvm-7.0/clang-7.0/work/llvm-7.0.0rc2.src/projects/compiler-rt/lib/xray/xray_basic_logging.cc:320:36: error: use of undeclared identifier 'CLOCK_REALTIME'
        int result = clock_gettime(CLOCK_REALTIME, &TS);
                                   ^
2 errors generated.
make[2]: *** [projects/compiler-rt/lib/xray/CMakeFiles/RTXrayBASIC.osx.dir/xray_basic_logging.cc.o] Error 1

[kencu (Ken)]

if XRAY is disabled, clang-7.0 builds through on 10.9 without further modifications (and without the map_anonymous patch):

$ port -v installed clang-7.0
The following ports are currently installed:
  clang-7.0 @7.0.0rc2_0+analyzer+libstdcxx (active) platform='darwin 13' archs='x86_64' date='2018-09-13T23:47:36-0700'

[kencu (Ken)]

A moderately complex replacement for clock_gettime() with an MIT license: <​https://gist.github.com/alfwatt/3588c5aa1f7a1ef7a3bb>.

[kencu (Ken)]

Here's a clock_gettime() replacement that is currently used in MacPorts, courtesy of Jeremy from 2016 (so presumably acceptable): <​https://github.com/macports/macports-ports/blob/master/graphics/cogl/files/patch-clock_gettime.diff>

[kencu (Ken)]

Upstream bug report for MAP_ANONYMOUS issue <​https://bugs.llvm.org/show_bug.cgi?id=38958>.

[kencu (Ken)]

Upstream bug report for clock_gettime() issue <​https://bugs.llvm.org/show_bug.cgi?id=38959>

[jeremyhu (Jeremy Huddleston Sequoia)]

Thanks for filing the upstream radars. We should just disable in on < 10.9 for now unless someone speaks up that they need it.

[jeremyhu (Jeremy Huddleston Sequoia)]

Re-assigning to Ken, so he can just update his existing patch for <10.6 instead.

[kencu (Ken)]

Will do. To avoid commit conflicts, I'll wait until <​https://github.com/macports/macports-ports/pull/2614> lands shortly.

[kencu (Ken)]

In bafb66e16d5ed7e0b3b70b1f1caf82a5b3068463/macports-ports (master):

clang-7.0: fix build on darwin 14 and less

XRAY currently does not build on these systesm due to the
issues mentioned in the Portfile
closes: #57130