Suppress llvm and knc issues.

@bradcray made a good suggestion that llvm and knc testing should use suppressions to track the
couple tests that are having issues. This updates the nightly testing scripts to suppress pidigits failures
for llvm and fileIO failures for knc.
It is probably defined, but it may not be where we want to find this file. For example, if $CHPL_HOME is set from the module or tarball install, `$CHPL_HOME/test/Suppressions` will not exist.