[Chapel Merge] Print the original output when a prediff might hid

Branch: refs/heads/master
Revision: 161406f
Author: ronawho
Log Message:

Merge pull request #16332 from ronawho/print-comp-output-when-prediff

Print the original output when a prediff might hide compile errors

[reviewed by @gbtitus and @lydia-duncan]

Some of our prediffs grep for specific lines and discard everything
else. When compilation fails this results in hiding all the output,
so if compilation failed and there was a prediff print the original
output so it’s easier to triage.

Modified Files:
M util/test/sub_test

Compare: https://github.com/chapel-lang/chapel/compare/7e4be62b7535...161406f70942