[ARM] Fix for PR36577

Don't PerformSHLSimplify if the given node is used by a node that also uses a
constant because we may get stuck in an infinite combine loop.

bugzilla: https://bugs.llvm.org/show_bug.cgi?id=36577

Patch by Sam Parker.

Differential Revision: https://reviews.llvm.org/D44097

llvm-svn: 326882