The addition of `addDeclErr` introduced a memory leak at every call
site, and I also would like to push back on having more than 1
compilation error per `Decl`.
This reverts commit 1634d45f1d53c8d7bfefa56ab4d2fa4cc8218b6d.
Use case:
zig build-exe non_existent_file.zig
Previous behavior:
error.FileNotFound, followed by an error return trace
Behavior after this commit:
error: unable to read non_existent_file.zig: FileNotFound
(end of stderr, exit code 1)
This turns AllErrors.Message into a tagged union which now has the
capability to represent both "plain" errors as well as source-based
errors (with file, line, column, byte offset). The "no entry point found"
error has moved to be a plain error message.
When we get a cache hit for a stage1 compilation, we need to know about
some of the flags such as have_winmain or have_dllmain to know which
subsystem to infer during linking.
To do this, we append a hex-encoded byte into the intentionally-dangling
symlink which contains the cache hash digest rather than a filename. The
hex-encoded byte contains the flags we need to infer the subsystem
during linking.
