Regression: exit non-zero if compilation fails
Enable more packages in llgo-dist

Also, remove the hack in llgo-dist for
skipping the junk in drone.io's std.
The drone.io job is now using a fresh
Go distribution.
Fix interface wrappers

Truncate intptr before coercing *int8 to
receiver type of fewer bits.

Also, remove redundant legacy code from value.go.