Provides very simple ConcurrentQueue and ThreadPool classes that build even when threading is disabled.
Also provides a `DeferredLogs` class that captures log output to be replayed on the main thread
later.
Conditionally include help source tracking to preserve ABI.
Docs builds can (and should) use `ENABLE_HELP_SOURCE` so that the generated sphinx docs can perform default grouping and link to source files.
Regular user-builds don't need the source tracking.
Use `chformal` as example, comparing the `autocmd` output with `ChformalPass::formal_help()`, the json dump from the `ContentListing`, the command line output, and the RST generated (using `autocmd_rst`).
Includes bullet points on each step for more information.
Should eventually end up in `yosys_internals/extending_yosys/contributing.rst`, but it currently lives in `cmd/index_internal.rst` to avoid merge conflicts since cell help documentation is still WIP.
Also exports chformal source and help output to `docs/source/generated` during `make docs/prep`.
Use `std::experimental::source_location` because clang support is `??`
Add `ENABLE_SOURCE_LOCATION` make variable and corresponding `YOSYS_ENABLE_SOURCE_LOCATION` define.
Dummy out the struct if disabled and check for null instead of using `#ifdef` blocks everywhere.
Define `PrettyHelp` class with methods for declaring different parts of help message.
Currently able to produce standard help messages as expected.
Updates chformal to use (only) the new help_v2.
Currently makes use of a global static to track the current help context, allowing register.h to live in blissful ignorance and instead rely on help_v2 implementations calling `auto *help = PrettyHelp::get_current();` and `return true;` to minimise impact on rebuilds (i.e. not requiring every source file to be recompiled).
