qtsystems module misses linker options for clang-cl

Module: qtsystems

Problem: The linking options for `win32-msvc` are not passed to `win32-clang-msvc`, which causes linking failure for clang-cl.

P.S. Should the submodule dependency of `qtsystems` be upgraded to `dev` for 5.15? There's also a fix about compile error for clang-cl. (f46977ae785632e52fc7212265f2e1e0d38565db: msvc: Fix build with less permissive compiler options)