[cmake] Include LLVM_LIBXML2_ENABLED in LLVMConfig.cmake, PR36006

Include the LLVM_LIBXML2_ENABLED cache variable in LLVMConfig.cmake
in order to make it available for other LLVM packages to query. This
is necessary to fix stand-alone testing of LLD.

Differential Revision: https://reviews.llvm.org/D42252

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322973 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed