On Windows, autolink advapi32 from Path.inc for CryptAcquireContextW

This allows llvm-tblgen to link successfully when compiling with clang.

Both MSBuild and CMake will automatically add advapi32 as part of a set
of other dlls comprising the win32 API to the link line, but CMake
doesn't do that when compiling with clang.  Until someone adds that info
to cmake upstream, this seems like a reasonable work around.