[GlobalISel] Only build expensive remarks if they're enabled. NFC.

r313390 taught 'allowExtraAnalysis' to check whether remarks are
enabled at all.  Use that to only do the expensive instruction printing
if they are.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@313552 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed