Fixes bug causing ReleaseSmall to fail on Windows.
Due to the change in default behavior of ReleaseSmall, debug info are
stripped by default. However because `Compile.create` still defaults to
null, `producesPdbFile` will report true for
`lib/std/Build/Step/InstallArtifact.zig` causing it to fail on copying a
file that does not exist. This commit change the default of strip
depending on `optimize`.
* build.zig: the result of b.option() can be assigned directly in many
cases thanks to the return type being an optional
* std.Build: make the build system aware of the
std.Build.Step.Compile.BuildId type when used as an option.
- remove extraneous newlines in error logs
* simplify caching logic
* simplify hexstring parsing tests and use a doc test
* simplify hashing logic. don't use an optional when the `none` tag
already provides this meaning.
* CLI: fix incorrect linker arg parsing
