Ensure that the compiler recognizes dead code containing constant
empty arrays. This avoids new compilation failures in the pmap
open coding tests.

Also fixes the same tests on other implementations when the compiler
signals differently or when the generated code signals differently,
namely when the global optimization setting is high.

As a result of the migration from sourceforge, the bug report
no longer exists. Failure case was:

(compile nil '(lambda () (the (values &optional) (values))))

A given error is transferred to only one thread.