These warnings were always enabled, but we didn't see them due to https://gitlab.com/OpenMW/openmw/-/issues/7882.
I do not fully understand the cause of 7822 as I can't repro it in a minimal CMake project.
Some of these fixes are thought through.
Some are sensible best guesses.
Some are kind of a stab in the dark as I don't know whether there was a
possible bug the warning was telling me about that I've done nothing to
help by introducing a static_cast.
Nearly all of these warnings were about some kind of narrowing
conversion, so I'm not sure why they weren't firing with GCC and Clang,
which have -Wall -Wextra -pedantic set, which should imply -Wnarrowing,
and they can't have been affected by 7882.
There were also some warnings being triggered from Boost code.
The vast majority of library headers that do questionable things weren't
firing warnings off, but for some reason, /external:I wasn't putting
these Boost headers into external mode.
We need these warnings dealt with one way or another so we can switch
the default Windows CI from MSBuild (which doesn't do ccache) to Ninja
(which does).
I have the necessary magic for that on a branch, but the branch won't
build because of these warnings.
They're needed on MacOS as SDL_opengl_gletx.h doesn't define them there.
They don't actually work on MacOS, so long-term, the code that uses
these defines should be changed to use #ifdef to check they're available
before using them.
As well as fixing the MacOS build, it meddled with a bunch of files that
already did the right thing.
This reverts commit 8162541a14b4b87d582acb13a0f2d2cc19415014, reversing
changes made to e16c451d0899c06047d3af41ab0b34990f245bfb.
