Fix an unused variable warning

(cherry picked from commit ea9850b)

Author: zmodem

llvm/lib/Target/ARM/ARMConstantIslandPass.cpp

@@ -330,8 +330,8 @@ void ARMConstantIslands::verify() {
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 /// print block size and offset information - debugging
 LLVM_DUMP_METHOD void ARMConstantIslands::dumpBBs() {
-  BBInfoVector &BBInfo = BBUtils->getBBInfo();
   LLVM_DEBUG({
+    BBInfoVector &BBInfo = BBUtils->getBBInfo();
     for (unsigned J = 0, E = BBInfo.size(); J !=E; ++J) {
       const BasicBlockInfo &BBI = BBInfo[J];
       dbgs() << format("%08x %bb.%u\t", BBI.Offset, J)