Use same set of headers in default mode and mutant-tracking mode

[JonathanFoo0523]

Previously, dredd included different sets of headers for default mode
and mutant-tracking mode. This could alter macro definitions and lead to
the manual insertion of void __dredd_prelude_start(); in one mode but
not the other. To ensure consistency across both modes, Dredd now emits
the union of headers from both modes.

Fixes #342 .

[JonathanFoo0523]

@afd seems like the window build failed because stdatomic.h is an experimental feature for MSVC:
https://developercommunity.visualstudio.com/t/VS2022-1754:-stdatomich:-Compile-erro/10351339

The workaround is adding /experimental:c11atomics flag.

Could you let me know where to modify the workflow script to add MSVC compiler flag? Is it this line here?

[afd]

From the CI logs I see:

cl.exe '/std:c17 /experimental:c11atomics' -c add.c

It looks like the two flags are being passed as if they were a single flag, due to the use of quotes. Hopefully if the quotes are eliminated this will work.

[afd]

Looks good but some changes suggested.