mac autoconf: support current and future SDKs

[philburk]

Improve the way we generate the path to the SDK so that it
it not tied to specific versions.

Also changed macosx-version-min to 10.6

Fixes #378
Fixes #468

[Be-ing]

I assume you've tested this locally on macOS 11? It doesn't seem that you're running any macOS CI??

[philburk]

Yes, I tested locally on Big Sur with XCode 12.3. We should add some Mac CI.

[Be-ing]

I already added macOS CI in #459.

[Be-ing]

This change looks good to me. Is there anything else that needs to be taken care of before releasing?

[philburk]

@jmelas - I see that in #359 you suggested:

mac_sysroot="-isysroot $(xcrun --sdk macosx --show-sdk-path)"

How does that compare to using xcodebuild like I did in this script?

[jmelas]

@jmelas - I see that in #359 you suggested:

mac_sysroot="-isysroot $(xcrun --sdk macosx --show-sdk-path)"

How does that compare to using xcodebuild like I did in this script?

Hi @philburk
In my machine the command
xcrun --sdk macosx --show-sdk-path
executes much faster than
xcodebuild -version -sdk macosx Path

[philburk]

Thanks jmelas. I switched to xcrun.

[RossBencina]

I can't easily test these changes right now, but if you have multiple people saying that the changes work, then I see no reason to hold off on merging.