compiler: Do not look up fail in RnExpr if bind pattern is irrefutible.

Adds a check in `rnStmt`, in sub-expr `getFailFunction`, to determine if
the pattern of a bind statement is irrefutible. If so, skip looking up
the `fail` name.

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie

GHC Trac Issues: #13649

Differential Revision: https://phabricator.haskell.org/D3553

(cherry picked from commit 2fcb5c5c)