[X86] Fix gcc7 -Wunused-but-set-variable warning. NFCI.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@350701 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 62afcb7..64e6fb9 100644
--- a/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -540,7 +540,6 @@
     unsigned InstrOffset = 0;
     unsigned StackAdjust = 0;
     unsigned StackSize = 0;
-    unsigned PrevStackSize = 0;
     unsigned NumDefCFAOffsets = 0;
 
     for (unsigned i = 0, e = Instrs.size(); i != e; ++i) {
@@ -588,7 +587,6 @@
         //  L0:
         //     .cfi_def_cfa_offset 80
         //
-        PrevStackSize = StackSize;
         StackSize = std::abs(Inst.getOffset()) / StackDivide;
         ++NumDefCFAOffsets;
         break;