[PECOFF] Fix DLLCharacteristics field.

IMAGE_DLL_CHARACTERISTICS_NO_SEH flag should be set only when SEH is disabled.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@202215 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Add a utility function to add DIR32 relocation.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@202217 91177308-0d34-0410-b5e6-96231b3b80d8