[clang] [compiler-rt] [nsan] Add shared runtime (PR #98415)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> > It seems to cause a build failure:
> > [lab.llvm.org/buildbot](https://lab.llvm.org/buildbot/#/builders/123/builds/1580)
> 
> It seems the issue was due to old system linker. If I use lld to build compier-rt the build passes. I will fix the buildbot [llvm/llvm-zorg#225](https://github.com/llvm/llvm-zorg/pull/225)

Thanks. This is a real issue that GNU ld doesn't like `.preinit_array` in DSO. I've fixed forward by adding `nsan_preinit.cpp`

https://github.com/llvm/llvm-project/pull/98415