[clangd] Skip ClangdVFSTest.TestStackOverflow when address sanitizer is used

Summary:
The ClangdVFSTest.TestStackOverflow unittest does not seem to work
when building the test with address sanitizer activated. Afaict the
goal is to get a constexpr depth error, rather than stack overflow.
But with asan instrumentation we do get stack overflow complaints
from asan. As a workaround this patch simply disables the test case,
when being built with address sanitizer activated.

Reviewers: sammccall, Dmitry.Kozhevnikov

Reviewed By: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits, llvm-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D76533