cross platform: fix platform endianness check
cross platform: fix platform endianness check

By default(mostly), both `BIG_ENDIAN` and `LITTLE_ENDIAN` are defined
on *nix platforms. Unlike Windows, comparing the value of `BYTE_ORDER`
to `BIG_ENDIAN` or `LITTLE_ENDIAN` tells the endianness of the system.

I couldn’t see any other usage of `BIG_ENDIAN` definition, otherwise
macro could be located under a common header file.

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