[MERGE #2609 @obastemur] xplat: Improve ICU build options
[MERGE #2609 @obastemur] xplat: Improve ICU build options

Merge pull request #2609 from obastemur:icu_reduce

- optional ICUDATA dependency
- Default to --no-icu instead of icucore on OSX

mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore