Try to simplify cmake files using variables set by find_package

[thakis]

Summary

No intended behavior change.

See https://gitlab.kitware.com/cmake/cmake/-/merge_requests/1043
for some background. (LLVM requires CMake 3.13, so we are guaranteed
to have that change.)

[hans]

lgtm

But something seems to break every time someone touches this stuff, so we should be prepared for that :)

llvm/lib/Support/CMakeLists.txt

# System
   Demangle
   )
 
 set(llvm_system_libs ${system_libs})
 
 # 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_ZLIB)
-  # CMAKE_BUILD_TYPE is only meaningful to single-configuration generators.
-  if(CMAKE_BUILD_TYPE)
-    string(TOUPPER ${CMAKE_BUILD_TYPE} build_type)
-    get_property(zlib_library TARGET ZLIB::ZLIB PROPERTY LOCATION_${build_type})
-  endif()
-  if(NOT zlib_library)
-    get_property(zlib_library TARGET ZLIB::ZLIB PROPERTY LOCATION)
-  endif()
-  get_library_name(${zlib_library} zlib_library)
-  set(llvm_system_libs ${llvm_system_libs} "${zlib_library}")
+  get_library_name(${ZLIB_LIBRARY} zlib_library_name)
+  set(llvm_system_libs ${llvm_system_libs} "${zlib_library_name}")
 endif()
 
 if(LLVM_ENABLE_TERMINFO)
   if(NOT terminfo_library)
     get_property(terminfo_library TARGET Terminfo::terminfo PROPERTY LOCATION)
   endif()
   get_library_name(${terminfo_library} terminfo_library)
   set(llvm_system_libs ${llvm_system_libs} "${terminfo_library}")

llvm/lib/WindowsManifest/CMakeLists.txt

 include(GetLibraryName)
 
 if(LLVM_ENABLE_LIBXML2)
-  set(imported_libs LibXml2::LibXml2)
+  set(imported_libs "${LIBXML2_LIBRARIES}")
 endif()
 
 add_llvm_component_library(LLVMWindowsManifest
   WindowsManifestMerger.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/WindowsManifest
   ${Backtrace_INCLUDE_DIRS}
 
   LINK_LIBS
   ${imported_libs}
 
   LINK_COMPONENTS
   Support
   )
 
 # 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 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 ${libxml2_library})
+  get_library_name(${LIBXML2_LIBRARY} libxml2_library_name)
+  set_property(TARGET LLVMWindowsManifest PROPERTY LLVM_SYSTEM_LIBS ${libxml2_library_name})
 endif()