bug#27810: macOS runtime feature detection

[Richard Stallman]

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  > I’m afraid I don’t understand why it’s a problem for cross
  > compilation. At the moment we don’t even provide any way of building
  > Emacs on one version of macOS that is guaranteed to work on another
  > version of macOS, never mind cross‐compiling the NS port from another
  > platform.

Supporting cross-compilation is a general goal for GNU packages.
That's why we make a point, in general, to use compile time
for autoconf tests.

-- 
Dr Richard Stallman
President, Free Software Foundation (gnu.org, fsf.org)
Internet Hall-of-Famer (internethalloffame.org)
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