[llvm] [gn build] Port win asan runtime rules (PR #108293)

[Nico Weber via llvm-commits]

nico wrote:

Right, see here: 

https://github.com/llvm/llvm-project/commit/53a81d4d26f0409de8a0655d7af90f2bea222a12#diff-e07727916fd4838a70b92fe6a62b5c6b52b8db246579951b16498628091e05c1R105

```
if(MSVC)
  # asan on windows only supports the release dll version of the runtimes, in the interest of
  # only having one asan dll to support/test. Having asan statically linked
  # with the runtime might be possible, but it multiplies the number of scenerios to test.
  # the program USING sanitizers can use whatever version of the runtime it wants to.
  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreadedDLL)
endif()
```

https://github.com/llvm/llvm-project/pull/108293