linux: Fix compile using GCC

[kphillisjr]

This is sort of a big request, but fix compilation using GCC (version 5.4.0) on Ubuntu 16.04 LTS. Many Linux distributions use GCC as the default compiler.

[dilijev]

This is out of scope for our current milestones and current roadmap but we'll keep this in mind. During our initial work bringing ChakraCore cross-platform, we decided it was best to focus on a single compiler toolchain.

You should be able to install a compatible version of clang on most distributions so this shouldn't be a blocking issue for you. :)

[obastemur]

As @dilijev mentioned, this is not one of the priorities we have at hand due to Clang does the job very well. However, supporting GCC would be really nice!

Added Accepting PRs on this. If there are community member(s) want to contribute fixes to GCC build (partially is also accepted) we would love to have them.