[MacPorts] #58260: libgcc8 build fails due to "Atomic" error on Mojave

[MacPorts]

#58260: libgcc8 build fails due to "Atomic" error on Mojave
--------------------------+---------------------
 Reporter:  physicsbeany  |      Owner:  (none)
     Type:  defect        |     Status:  new
 Priority:  Normal        |  Milestone:
Component:  ports         |    Version:  2.5.4
 Keywords:  atomic        |       Port:  libgcc8
--------------------------+---------------------
 Recently upgraded to MacOS Mojave from High Sierra, and followed general
 Macports instructions for migrating my old ports. Things went fine until
 libgcc8 (needed to do my py27-scipy installation). Initially, this failed
 because of Unwind issues. I solved this by following the advice in ticket
 #57198.

 Now, however, the compilation fails because of an "Atomic" error.
 Specifically, the first instance of the Error in the log file is:


 {{{
 :info:build
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/sys/ucred.h:94:2:
 error: '_Atomic' does not name a type
 :info:build   _Atomic u_long          cr_ref;  /* reference count */
 }}}

 Full logfile attached

 Some Googling indicates that this may be avoided by defining
 __STDC_NO_ATOMICS__, but I'm not certain this is the right answer (and I
 don't know how to do this as part of a Macports installation).

-- 
Ticket URL: <https://trac.macports.org/ticket/58260>
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