Improve compilation times on Windows

[vittorioromeo]

Thank you for the very useful library!

Few improvements:

• Better header hygiene
• Isolate windows.h to .cpp whenever possible
• Use WIN32_LEAN_AND_MEAN
• Remove unused headers

Tested on Windows with

cmake .. -DCMAKE_BUILD_TYPE=Debug -GNinja -DCMAKE_EXPORT_COMPILE_COMMANDS=1 
  -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_CXX_FLAGS="-ftime-trace -Wall -Wextra -Wpedantic 
  -Wno-ignored-attributes" -DCMAKE_COLOR_DIAGNOSTICS=1 -DCPPTRACE_BUILD_TESTING=1 
  -DCPPTRACE_BUILD_BENCHMARKING=0

There's a lot more that can be improved if you are interested.

[jeremy-rifkin]

Thanks for taking the time to contribute! Header hygiene is always appreciated, as is tidying up includes. I definitely agree there's a lot more that can be improved 😄 I have a small handful of comments, mostly straightforward

[jeremy-rifkin]

Can we #include <cpptrace/cpptrace.hpp> here instead. My main concern is this falling out of line with the definition there.

[vittorioromeo]

I measured this change making a noticeable difference via ClangBuildAnalyzer. If there is a mismatch between these forward declarations and cpptrace.hpp, compilation will fail with an hard error (i.e. you won't silently introduce any UB).

Given that, would you reconsider?

[jeremy-rifkin]

I think that’s reasonable, I appreciate you measuring. I had also been thinking of splitting ip the cpptrace.hpp file so one option in the future might be to have a more minimal header providing the type.

[jeremy-rifkin]

Do you think it'd be worthwhile to just do target_compile_definitions(... PRIVATE WIN32_LEAN_AND_MEAN)?

[jeremy-rifkin]

Looks like some CI is failing, unfortunately one of the hard things about developing this library is how much code can't be tested on a single platform. Happy to help however I can.

[vittorioromeo]

@jeremy-rifkin: could CI be retriggered, please?

[vittorioromeo]

@jeremy-rifkin: and again please :)

If possible, could you make CI not require approval until this PR is merged? I need to iterate a bit to figure out what includes are missing on various platforms.

[jeremy-rifkin]

I’ll look to see if I can set it to not need approval, sorry for the iteration hassle

[vittorioromeo]

I’ll look to see if I can set it to not need approval, sorry for the iteration hassle

Seems like approval is still required :(

[jeremy-rifkin]

Sorry for the hassle here, I think the setting is correct now. I can take a stab at getting things correct later too.

[jeremy-rifkin]

Thanks again so much for the contribution, taking the time to do this, and putting up with all the iteration pain. I went ahead and added a couple commits to get remaining stuff working. Everything here LGTM, thanks again!