Summary:
Proposed header (or its dir) is a single place to put MSVC/GCC hacks. So
far it only includes the COMPOUND_LITERAL macro which behaves differently
depending on MSVC mode.
When MSVC2015 is used in C++ mode, it does not support things like:
`(my_type) {initializers}`, but in C mode it does.
To clarify: I am not even sure whether we need to have the ability to compile in a purely C mode, but I did not want to figure out.
Test Plan: - on Linux, run `python setup.py build`, run all the tests, see them passing
Reviewers: #sourcecontrol, tja
Reviewed By: tja
Subscribers: tja, jsgf, mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D4843230
Signature: t1:4843230:1491496062:3fa10ae5a5aac850689991de1ca6ee1ac86d9dce