* Eliminate all uses of `std.debug.print` in make() functions, instead
properly using the step failure reporting mechanism.
* Introduce the concept of skipped build steps. These do not cause the
build to fail, and they do allow their dependants to run.
* RunStep gains a new flag, `skip_foreign_checks` which causes the
RunStep to be skipped if stdio mode is `check` and the binary cannot
be executed due to it being a foreign executable.
- RunStep is improved to automatically use known interpreters to
execute binaries if possible (integrating with flags such as
-fqemu and -fwasmtime). It only does this after attempting a native
execution and receiving a "exec file format" error.
- Update RunStep to use an ArrayList for the checks rather than this
ad-hoc reallocation/copying mechanism.
- `expectStdOutEqual` now also implicitly adds an exit_code==0 check
if there is not already an expected termination. This matches
previously expected behavior from older API and can be overridden by
directly setting the checks array.
* Add `dest_sub_path` to `InstallArtifactStep` which allows choosing an
arbitrary subdirectory relative to the prefix, as well as overriding
the basename.
- Delete the custom InstallWithRename step that I found deep in the
test/ directory.
* WriteFileStep will now update its step display name after the first
file is added.
* Add missing stdout checks to various standalone test case build
scripts.
* Step.init() now takes an options struct
* Step.init() now captures a small stack trace and stores it in the
Step so that it can be accessed when printing user-friendly debugging
information, including the lines of code that created the step in
question.
Changes only pertain arm64 as for x86_64 turns out we are
missing one additional feature which is synthesising unwind info
from only eh frame records, or at least this is what it looks like
when I analysed the output of Apple's ld.
