[clangd] Attempt to fix failing Windows buildbots.

The assertion is failing on Windows, probably because path separator is different.

For the failure see:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/28072/steps/test/logs/stdio

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@371422 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed