[clang][flang][windows] Prefer user-provided library paths (-L) (#90758)

Currently the paths to compiler-rt and the Flang runtimes from the LLVM
build/install directory are preferred over any user-provided library
paths. This means a user can't override compiler-rt or the Flang
runtimes with custom versions.

This patch changes the link order to prefer library paths specified with
-L over the LLVM paths. This matches the behaviour of clang and flang on
Linux.