Instead of storing an increasing version number in relevant packages
(compiler.Version, interp.Version, cgo.Version, ...), read the build ID
from the currently running executable. This has several benefits:
* All changes relevant to the compiled packages are caught.
* No need to bump the version for each change to these packages.
This avoids merge conflicts.
* During development, `go install` is enough. No need to run
`tinygo clean` all the time.
Of course, the drawback is that it might be updated a bit more often
than necessary but I think the overall benefit is big.
Regular release users shouldn't see any difference. Because the tinygo
binary stays the same, the cache works well.
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