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

Author: zmodem

tools/llvm-config/CMakeLists.txt

@@ -9,8 +9,9 @@ add_llvm_tool(llvm-config
   )
 
 # Compute the substitution values for various items.
-get_property(LLVM_SYSTEM_LIBS_LIST TARGET LLVMSupport PROPERTY LLVM_SYSTEM_LIBS)
-foreach(l ${LLVM_SYSTEM_LIBS_LIST})
+get_property(SUPPORT_SYSTEM_LIBS TARGET LLVMSupport PROPERTY LLVM_SYSTEM_LIBS)
+get_property(WINDOWSMANIFEST_SYSTEM_LIBS TARGET LLVMWindowsManifest PROPERTY LLVM_SYSTEM_LIBS)
+foreach(l ${SUPPORT_SYSTEM_LIBS} ${WINDOWSMANIFEST_SYSTEM_LIBS})
   if(MSVC)
     set(SYSTEM_LIBS ${SYSTEM_LIBS} "${l}.lib")
   else()