Tracking issue: enable more MSVC warnings

[GrabYourPitchforks]

Initial cost estimate: 1 week
Initial contacts: @trylek, @GrabYourPitchforks, @janvorli

We enable the following warning codes (as error) on some internal runs as part of compliance checks. The warnings are reviewed by hand. The manual reviews always show that we're ok, but it would be nice if we could turn these on as part of the public build. There's a little bit of work involved here to make things compile cleanly. But it would save us the trouble of running through manual review every release.

add_compile_options(/we4018)
add_compile_options(/we4055)
add_compile_options(/we4146)
add_compile_options(/we4242)
add_compile_options(/we4244)
add_compile_options(/we4267)
add_compile_options(/we4302)
add_compile_options(/we4308)
add_compile_options(/we4509)
add_compile_options(/we4510)
add_compile_options(/we4532)
add_compile_options(/we4533)
add_compile_options(/we4610)
add_compile_options(/we4611)
add_compile_options(/we4700)
add_compile_options(/we4701)
add_compile_options(/we4703)
add_compile_options(/we4789)
add_compile_options(/we4995)
add_compile_options(/we4996)

[jkotas]

We set warning level 3 at

runtime/eng/native/configurecompiler.cmake

Line 482 in 8a4d712

add_compile_options($<$<COMPILE_LANGUAGE:C,CXX>:/W3>) # set warning level to 3

. Majority of the warnings in this list are warning levels 1-3, so they should be enabled by default.

The clrcompression build is one exception that is not using the central setting and disables all warnings: https://github.com/dotnet/runtime/blob/master/src/libraries/Native/Windows/CMakeLists.txt#L4 . Maybe you are seeing this flagged because of that?