Try fixing the SDK path (your invalid):
$ xcrun --show-sdk-path --sdk macosx
You may have this result:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
Switch the default SDK location by calling:
$ sudo xcode-select -switch /Applications/Xcode.app/Contents/Developer
If this does not work, look inside the (normal) SDK path:
$ ls -lat /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/
You should see the SDK in this directory; if not, you will need to download them.
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