Disable warning 4530 for MSVC builds.

We compile with exceptions off for LLVM and all other LLVM
subprojects, so this brings parity to LLD and disables this
warning.

Reviewed by: Rui Ueyama

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@223131 91177308-0d34-0410-b5e6-96231b3b80d8