clang-cl: Ignore /Zc:inline and /Zc:rvalueCast

These flags enable behavior in MSVC that Clang has by default.

/Zc:inline essentially marks all COMDATs as discardable.  In LLVM
parlance, this means using linkonce_odr linkage, which is what we
already do.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@212117 91177308-0d34-0410-b5e6-96231b3b80d8