overhaul exit codes for rustc and rustdoc
This commit changes the exit status of rustc to 1 in the presence of
compilation errors. In the event of an unexpected panic (ICE) the
standard panic error exit status of 101 remains.
A run-make test is added to ensure that the exit code does not regress,
and compiletest is updated to check for an exit status of 1 or 101,
depending on the mode and suite.
This is a breaking change for custom drivers.
Note that while changes were made to the rustdoc binary, there is no
intended behavior change. rustdoc errors (i.e., failed lints) will still
report 101. While this could *also* hide potential ICEs, I will leave
that work to a future PR.
Fixes#51971.
a8247dd5c6