Xcode 11 & SDKROOT on macOS 10.14

[Aaron Madlon-Kay]

> xcrun can't find cdtool on my system even without specifying an SDK:

I don't know anything about it except that the error occurs when using
CLT and doesn't happen when using the Xcode SDK.

> The Xcode tools are another matter, and we should be setting DEVELOPER_DIR correctly to allow them to be found.

What would the correct value be?

Googling around I found e.g.
DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer (or other
Xcode installation, presumably). Used as either an envar or an
argument to xcodebuild, I could not find a value that allowed the
build to complete successfully when the SDKROOT was using the CLT.

-Aaron