* remove std.Build.updateFile. I noticed some people use it from
build.zig (declare phase) when it is intended only for use in the
make phase.
- This also was incorrectly reporting errors with std.log.
* std.Build.InstallArtifactStep
- report better errors on failure
- report whether the step was cached or not
* std.Build.InstallDirStep: report better error on failure
* std.Build.InstallFileStep: report better error on failure
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