[llvm] Fix typo for libxml2 detection

[sthibaul]

Summary

This seems to be a copy-paste from the similar zlib detection code.

[phosek]

LGTM

[sthibaul]

This is still not showing up on https://github.com/llvm/llvm-project/blob/main/llvm/lib/WindowsManifest/CMakeLists.txt , is there some more steps needed from my side?

[phosek]

I can push the change for you if you don't have commit permissions. What name and email would you like me to use?

[sthibaul]

yes, please, Samuel Thibault <[e-mail]> will be fine, thanks

llvm/lib/WindowsManifest/CMakeLists.txt

 # This block is only needed for llvm-config. When we deprecate llvm-config and
 # move to using CMake export, this block can be removed.
 if(LLVM_ENABLE_LIBXML2)
   # CMAKE_BUILD_TYPE is only meaningful to single-configuration generators.
   if(CMAKE_BUILD_TYPE)
     string(TOUPPER ${CMAKE_BUILD_TYPE} build_type)
     get_property(libxml2_library TARGET LibXml2::LibXml2 PROPERTY LOCATION_${build_type})
   endif()
-  if(NOT zlib_library)
+  if(NOT libxml2_library)
     get_property(libxml2_library TARGET LibXml2::LibXml2 PROPERTY LOCATION)
   endif()
   get_library_name(${libxml2_library} libxml2_library)
   set_property(TARGET LLVMWindowsManifest PROPERTY LLVM_SYSTEM_LIBS ${libxml2_library})
 endif()