Fix the way to check OS version

[ichizok]

Improved #659

When MACOSX_DEPLOYMENT_TARGET is prior than 10.10, we can check OS version by reading ProductVersion from /System/Library/CoreServices/SystemVersion.plist.

[splhack]

if ([NSProcessInfo instancesRespondToSelector:@selector(isOperatingSystemAtLeastVersion:)]) {
  NSOperatingSystemVersion version = {10, 13, 0};
  is_macos_high_sierra_or_later = [[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:version];	
}

[ichizok]

Thank you, I updated.

[splhack]

Sorry, I meant we don't need check_system_version method, specially the SystemVersion.plist part since isOperatingSystemAtLeastVersion: is available on 10.10 or later.

[ichizok]

When build MacVim with env MACOSX_DEPLOYMENT_TARGET < 10.10 (.travis.yml has set =10.8) isOperatingSystemAtLeastVersion: isn't available, so cannot build.
Therefore SystemVersion.plist part is needed in order to use MacVim built with env MACOSX_DEPLOYMENT_TARGET < 10.10 on 10.13.

[splhack]

I don't think we need to support that situation. Using SDK 10.9 or earlier and run the binary on 10.13 or later. It's overkill. We do support the latest Xcode + the latest SDK, and the binary could run on 10.8. Probably people can use SDK 10.8 for building MacVim for 10.8, but not for 10.13.

[splhack]

So the minimal code would look like

}

#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_10
    if ([[NSProcessInfo processInfo]
            respondsToSelector:@selector(isOperatingSystemAtLeastVersion:)])
    {
        NSOperatingSystemVersion version = {10, 13, 0};

        is_macos_high_sierra_or_later =
            [[NSProcessInfo processInfo] isOperatingSystemAtLeastVersion:version];
    }
#endif

    return OK;

[ichizok]

On travis build (MACOSX_DEPLOYMENT_TARGET=10.8), MAC_OS_X_VERSION_MAX_ALLOWED is MAC_OS_X_VERSION_10_8 so that code block is dropped.

[splhack]

Current master .travis.yml uses xcode9.2, so MAC_OS_X_VERSION_MAX_ALLOWED would be 10.12 or 10.13, and MAC_OS_X_VERSION_MIN_REQUIRED is 10.8 as MACOSX_DEPLOYMENT_TARGET in .travis.yml.

[ichizok]

Oh, MAC_OS_X_VERSION_MAX_ALLOWED... I saw wrong. OK, I understand.

[ichizok]

I updated.