This enables using to compile the code and then
link it using link.exe directly without invoking the linker through clang-cl.
It should hopefully make it easier for projects that don't use the compiler
to invoke the linker to use ASAN.
Generally we want to be careful about embedding full paths into the binary. While nobody is doing distributed builds today, in the future we want to support that.
What do you think of embedding just the basename into .drectve, and adding clang's resource dir to the LIB environment variable in the build system? That's a far less invasive change than making clang do the link step instead of link.exe, and should solve the problem.