It is better to manage warnings on our side to know what warnings we need to fix or suppress, and the only thing that header does is disabling deprecation warnings on MSVC and ICC which we would prefer to not show to users.
I have not touch examples because they are not affecting Spirit usage and testing dependencies, and modernizing them also seems like a waste of time when we encourage to start new projects with X3 instead of Qi.
Not intrusive. Significantly speeds up tests on MSVC (for about 3 times).
Finally solves exceeding build time limits on CI with MSVC compilers.
Did not set up PCH for X3, it is fast as-is (tooks only about 2 minutes).
Repository tests reuse PCH from Qi/Karma tests.
