Previously, the `test-stack-traces` step was essentially just testing
error traces, and even there we didn't have much coverage. This commit
solves that by splitting the "stack trace" tests into two separate
harnesses: the "stack trace" tests are for actual stack traces (i.e.
involving stack unwinding), while the "error trace" tests are
specifically for error return traces.
The "stack trace" tests will test different configurations of:
* `-lc`
* `-fPIE`
* `-fomit-frame-pointer`
* `-fllvm`
* unwind tables (currently disabled)
* strip debug info (currently disabled)
The main goal there is to test *stack unwinding* under different
conditions. Meanwhile, the "error trace" tests will test different
configurations of `-O` and `-fllvm`; the main goal here, aside from
checking that error traces themselves do not miscompile, is to check
whether debug info is still working even in optimized builds. Of course,
aggressive optimizations *can* thwart debug info no matter what, so as
before, there is a way to disable cases for specific targets / optimize
modes.
The program which converts stack traces into a more validatable format
by removing things like addresses (previously `check-stack-trace.zig`,
now `convert-stack-trace.zig`) has been rewritten and simplified. Also,
thanks to various fixes in this branch, several workarounds have become
unnecessary: for instance, we don't need to ignore the function name
printed in stack traces in release modes, because `std.debug.Dwarf` now
uses the correct DIE for inlined functions!
Neither `test-stack-traces` nor `test-error-traces` does general foreign
architecture testing, because it seems that (at least for now) external
executors often aren't particularly good at handling stack tracing
correctly (looking at you, Wine). Generally, they just test the native
target (this matches the old behavior of `test-stack-traces`). However,
there is one exception: when on an x86_64 or aarch64 host, we will also
test the 32-bit version (x86 or arm) if the OS supports it, because such
executables can be trivially tested without an external executor.
Oh, also, I wrote a bunch of stack trace tests. Previously there was,
erm, *one* test in `test-stack-traces` which wasn't for error traces.
Now there are a good few!
