Hexagon: Avoid unused variable warnings in Release builds.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185445 91177308-0d34-0410-b5e6-96231b3b80d8
Revert (most of) r185393 and r185395.

"Remove floating point computations form SpillPlacement.cpp."

These commits caused test failures in lencod on clang-native-arm-lnt.

I suspect these changes are only exposing an existing issue, but
reverting anyway to keep the bots passing while we investigate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185447 91177308-0d34-0410-b5e6-96231b3b80d8