Scavenging slots were only reserved when pseudo-instruction expansion in
frame lowering created new virtual registers. It is possible to still
need a scavenging slot even if no virtual registers were created, in cases
where the stack is large enough to overflow instruction offsets.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277355 91177308-0d34-0410-b5e6-96231b3b80d8
