[gn build] Port win asan runtime rules

[aeubanks]

Windows doesn't have a static runtime after #107899.

[nico]

See also 4a63d62 and 4d55f0b

I noticed that 53a81d4 passed /MD instead of /MT for a bunch of cflags and/or ldflags. I think we don't do that part in GN yet.

[aeubanks]

hmm I'm not seeing where the /MD//MT are. is that CMAKE_MSVC_RUNTIME_LIBRARY?

[nico]

Right, see here:

53a81d4#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()

[nico]

(...and ctrl-f "CMAKE_MSVC_RUNTIME_LIBRARY" for other instances in that diff.)