Checking only happens at compile time if -std=c++20 (or greater) is enabled. Otherwise
the checking happens at run time.
This requires the format string to be a compile-time constant (when compiling with
C++20), so fix a few places where that isn't true.
The format string behavior is a bit more lenient than C printf. For %d/%u
you can pass any integer type and it will be converted and output without
truncating bits, i.e. any length specifier is ignored and the conversion is
always treated as 'll'. Any truncation needs to be done by casting the argument itself.
For %f/%g you can pass anything that converts to double, including integers.
Performance results with clang 19 -O3 on Linux:
```
hyperfine './yosys -dp "read_rtlil /usr/local/google/home/rocallahan/Downloads/jpeg.synth.il; dump"'
```
C++17 before: Time (mean ± σ): 101.3 ms ± 0.8 ms [User: 85.6 ms, System: 15.6 ms]
C++17 after: Time (mean ± σ): 98.4 ms ± 1.2 ms [User: 82.1 ms, System: 16.1 ms]
C++20 before: Time (mean ± σ): 100.9 ms ± 1.1 ms [User: 87.0 ms, System: 13.8 ms]
C++20 after: Time (mean ± σ): 97.8 ms ± 1.4 ms [User: 83.1 ms, System: 14.7 ms]
The generated code is reasonably efficient. E.g. with clang 19, `stringf()` with a format
with no %% escapes and no other parameters (a weirdly common case) often compiles to a fully
inlined `std::string` construction. In general the format string parsing is often (not always)
compiled away.
Update experimental pass warnings to use a shared function. Reduces repetition, and also allows all of the warning flags to be combined (which at present is just experimental and the new internal).
Update `test_*` passes to call `internal()` in their constructors.
Change `top` pointer default to `nullptr` to avoid issues with `Design->top_module()` only operating on the current selection.
Calls to other passes (`bmuxmap` etc) will only operate on the current selection, and may cause problems when those cells are unprocessed, but this is consistent with the other backends that only operate on the full designs and will hopefully be fixed in another PR soon :)
`$extern:...` modules inserted by `techmap -extern` are special in the
regard that they have a private ID (starting with a dollar sign) but are
not an internal cell. Support those modules in xaiger export.
- Remove unused statics CONST_FALSE and CONST_TRUE (which appear to have been folded into the `Index` declaration as CFALSE and CTRUE).
- Assign default value of EMPTY_LIT to `a` and `b` for comparison ops.
- Tag debug only variables with YS_MAYBE_UNUSED, don't assign unused variables (but continue to call the function because it moves the file pointer).
`Const::size()` returns int, so change iterators that use it to `auto` instead of `size_t`.
For cases where size is being explicitly cast to `int`, use the wrapper that we already have instead: `Yosys::GetSize()`.
