rts/Timer: Actually fix #9105
rts/Timer: Actually fix #9105

jberthold astutely pointed out that the previous fix (D1822) could not
have possibly fixed the issue as the patch would only have had any
effect if !PROFILING.

Test Plan: Check for reduced CPU usage when compiled with `-prof` but
without `+RTS -p`

Reviewers: simonmar, austin, jberthold

Reviewed By: simonmar, jberthold

Subscribers: simonmar, thomie

Differential Revision: https://phabricator.haskell.org/D1844

GHC Trac Issues: #9105

(cherry picked from commit 1c6130d91420dc835c281bc9b13d603b7aa49b59)

GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc