10.11 SDK on Xcode 8.3.3: "SDK not found"
Xcodelegacy.sh installed the 10.11 SDK in the right place within my Xcode.app folder.
However, when I chang the Base SDK from macosx10.12 to macosx10.11, when I dismiss the popup the Base SDK setting is "macosx10.11 (SDK not found)"
I speculate that I need the 10.11 SDK because the 10.12 is not correctly building my kernel extension. kextutil on 10.11 complains that my kext is missing a function symbol.
which popup did you dismiss? In Xcode, the choice should be "OS X 10.11" and should appear in the popup menu. All installed SDKs should appear, and you shouldn't have to type the SDK name manually. Also note that you have to reinstall all SDKs after an Xcode upgrade. This is probably the issue here. Did you install Xcode 9 beta? Or recently upgraded from 8.3.2?
here's what the menu should look like (I have 10.4, 10.5, 10.6, 10.11 installed)

My apologies, it has been a year since I last logged in to GitHub. If you still have a question for me, please let me know and I will reply expeditiously.
The question is: do you still have that issue?
Hu