[PECOFF] Use "llvm-readobj -coff-imports" to test the import table.

-coff-imports is added in r218915. You may have to sync your llvm source tree.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@218919 91177308-0d34-0410-b5e6-96231b3b80d8