message: Get sysroot path in a robust way for nsync ios build
  * Get sysroot in a robust way for nsync ios build
  * cleanup useless variable
  cleaned `xcode`
diff: @@ -127,16 +127,16 @@ for arch in $archs; do
  include dependfile
  ';;
  - ios) xcode=/Applications/Xcode.app/Contents/Developer/Platforms
  + ios)
  arch_flags=
  case "$arch" in
  i386|x86_64)
  arch_flags="$arch_flags -mios-simulator-version-min=8.0"
  - arch_flags="$arch_flags -isysroot $xcode/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.0.sdk"
  + arch_flags="$arch_flags -isysroot `xcrun --sdk iphonesimulator --show-sdk-path`"
  ;;
  *)
  arch_flags="$arch_flags -miphoneos-version-min=8.0"
  - arch_flags="$arch_flags -isysroot $xcode/iPhoneOS.platform/Developer/SDKs/iPhoneOS10.0.sdk"
  + arch_flags="$arch_flags -isysroot `xcrun --sdk iphoneos --show-sdk-path`"
  ;;
  esac
  makefile='
  