Fix build with expensive checks enabled

Include of llvm/IR/Verifier.h was removed from HexagonCommonGEP.cpp in r289604
as unused. In fact it is required when expensive checks are enabled, because
it declared function `verifyFunction`, which is called in conditionally compiled
part of the file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290170 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed