X86FrameLowering: Fix getFrameIndexReference() for 'fixed' objects

Debug information is calculated with getFrameIndexReference() which was
missing some logic for the fixed object cases (= parameters on the stack).

rdar://24557797

Differential Revision: https://reviews.llvm.org/D32204

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300781 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed