[clang-cl] Do not allow using both /Zc:dllexportInlines- and /fallback flag

Summary: /Zc:dllexportInlines with /fallback may cause unexpected linker error. It is better to disallow compile rather than warn for this combination.

Reviewers: hans, thakis

Reviewed By: hans

Subscribers: cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D54426

llvm-svn: 346733