[MacPorts] #55006: Can't build zsh on 10.13

[MacPorts]

#55006: Can't build zsh on 10.13
--------------------+-------------------
 Reporter:  kjyv    |      Owner:
     Type:  defect  |     Status:  new
 Priority:  Normal  |  Milestone:
Component:  ports   |    Version:  2.4.1
 Keywords:          |       Port:
--------------------+-------------------
 Not sure how this worked in previous osx versions (it did for me), but
 from https://stackoverflow.com/questions/5167269/clock-gettime-
 alternative-in-mac-os-x it seems that this function is not available. Or
 should be from 10.12 but the wrong time.h is used.

 {{{
 :info:build make[3]: Entering directory
 `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_shells_zsh/zsh/w
 ork/zsh-5.4.2/Src/Modules'
 :info:build /usr/bin/clang -c -I. -I../../Src -I../../Src -I../../Src/Zle
 -I. -I/opt/local/include -I/opt/local/include -DHAVE_CONFIG_H -DMODULE
 -pipe -Os -arch
 x86_64 -fno-common -o datetime..o datetime.c
 :info:build datetime.c:188:9: warning: implicit declaration of function
 'clock_gettime' is invalid in C99 [-Wimplicit-function-declaration]
 :info:build     if (clock_gettime(CLOCK_REALTIME, &now) < 0) {
 :info:build         ^
 :info:build datetime.c:188:23: error: use of undeclared identifier
 'CLOCK_REALTIME'
 :info:build     if (clock_gettime(CLOCK_REALTIME, &now) < 0) {
 :info:build                       ^
 :info:build datetime.c:214:23: error: use of undeclared identifier
 'CLOCK_REALTIME'
 :info:build     if (clock_gettime(CLOCK_REALTIME, &now) < 0) {
 :info:build                       ^
 :info:build 1 warning and 2 errors generated.
 :info:build make[3]: *** [datetime..o] Error 1
 }}}

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Ticket URL: <https://trac.macports.org/ticket/55006>
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