Re: Fix for configure error in 9.5/9.6 on macOS 11.0 Big Sur

Jesse Zhang <sbjesse@gmail.com> writes:
> Notice that -Werror=implicit-function-declaration up there? I spent a
> few minutes digging in Apple's published fork of LLVM, they've been
> forcing this error flag for quite a while, but this particular
> warning-turned-error is guarded by a conditional along the lines of "is
> this iOS-like" [1][2],

Wow, [1] is interesting:

    // For iOS and watchOS, also error about implicit function declarations,
    // as that can impact calling conventions.
    if (!isTargetMacOSBased())
      CC1Args.push_back("-Werror=implicit-function-declaration");

I wonder if the new Xcode version dropped the not-macOS restriction
on doing this?  It's not much of a stretch of the imagination
to guess that the iOS/watchOS issue is related to Apple's ABI
conventions for ARM, in which case they might have to do the
same for macOS to get it to run on ARM ... which we can expect
that Big Sur is ready for.

Anyway, I'm now satisfied that we understand where the problem really
lies, so +1 for back-patching 1c0cf52b39ca3.

            regards, tom lane