title: iphone sdk missing from xcrun how to build for iphone from command line?
body: <p>I'm trying to figure how to build metal shaders for iphone os using xcrun. 
  I have (the almost latest) Xcode 11.3.1 installed on macos 1.4 Mojave.</p>
  
  <p><code>xcrun --sdk iphoneos --show-sdk-path</code>
  reports that the sdk cannot be found.</p>
  
  <p>I checked
  <code>xcrun --sdk macosx --show-sdk-path</code>,
  which reports 
  /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk</p>
  
  <p>The iphone and TVOS sdks don't seem to be there at all. However, I'm able to use the Xcode IDE to build to an iphone. I checked the build logs and found that one step sets the SDKROOT to:
  <code>SDKROOT=/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS13.2.sdk</code> which is inside the Xcode bundle.</p>
  
  <p>I want to be able to build from the command line, but clearly the correct path hasn't been registered. Do I need to reinstall the command line tools, or is there some setting I need to add an SDK to xcrun?</p>
  
  <p>How do I proceed?</p>