CMake: Make libxml2 show up in --system-libs (PR36660)

lib/WindowsManifest/CMakeLists.txt adds it to LLVM_SYSTEM_LIBS on that
target, but it was never getting picked up in
tools/llvm-config/CMakeLists.txt.

Differential Revision: https://reviews.llvm.org/D44302

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327135 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed