move logic out of ci into ios builder script

.drone.jsonnet

@@ -298,9 +298,6 @@ local iphone_builder(name,
       environment: { SSH_KEY: { from_secret: 'SSH_KEY' } },
       commands: [
         'echo "Building on ${DRONE_STAGE_MACHINE}"',
-        // If you don't do this then the C compiler doesn't have an include path containing
-        // basic system headers.  WTF apple:
-        'export SDKROOT="$(xcrun --sdk iphoneos --show-sdk-path)"',
         'export CMAKE_BUILD_PARALLEL_LEVEL=6',
         'ulimit -n 1024',  // because macos sets ulimit to 256 for some reason yeah idk
         './contrib/ios.sh ' + ci_mirror_opts,

contrib/ios.sh

@@ -8,6 +8,8 @@ if ! [ -f LICENSE ] || ! [ -d llarp ]; then
     echo "You need to run this as ./contrib/ios.sh from the top-level lokinet project directory"
 fi
 
+unset SDKROOT
+export SDKROOT="$(xcrun --sdk iphoneos --show-sdk-path)"
 
 mkdir -p build/iphone/{sim,device}