[clangd] Force the required interpretation of #import on windows tests.

Summary: NFC but should fix a bunch of tests.

Reviewers: kadircet

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64857

llvm-svn: 366321