Revert "[CMake] Don't enable BUILD_WITH_INSTALL_RPATH when using custom build rpath"

[tambre]

Summary

This reverts commit 0ebc1fb29f278db0665423f15c53e6ee9601dddb.

The behaviour should have been the same as before unless specifying CMAKE_BUILD_RPATH,
which was previously broken.
However, this seems to have broken builds for some people that don't specify it.
Reverting until I can investigate.

llvm/cmake/modules/AddLLVM.cmake

macro(add_llvm_executable name)
   else()
     add_executable(${name} ${ALL_FILES})
   endif()
 
   setup_dependency_debugging(${name} ${LLVM_COMMON_DEPENDS})
 
   if(NOT ARG_NO_INSTALL_RPATH)
     llvm_setup_rpath(${name})
-  else()
-    # Enable BUILD_WITH_INSTALL_RPATH unless CMAKE_BUILD_RPATH is set.
-    if(NOT "${CMAKE_BUILD_RPATH}" STREQUAL "")
-      set_property(TARGET ${name} PROPERTY BUILD_WITH_INSTALL_RPATH ON)
-    endif()
-
-    set_property(TARGET ${name} PROPERTY INSTALL_RPATH "${LLVM_LOCAL_RPATH}")
+  elseif (LLVM_LOCAL_RPATH)
+    set_target_properties(${name} PROPERTIES
+                          BUILD_WITH_INSTALL_RPATH On
+                          INSTALL_RPATH "${LLVM_LOCAL_RPATH}")
   endif()
 
   if(DEFINED windows_resource_file)
     set_windows_version_resource_properties(${name} ${windows_resource_file})
   endif()
 
   # $<TARGET_OBJECTS> doesn't require compile flags.
   if(NOT LLVM_ENABLE_OBJLIB)
if(LLVM_LINKER_IS_GNULD)
       # $ORIGIN is not interpreted at link time by ld.bfd
       set_property(TARGET ${name} APPEND_STRING PROPERTY
                    LINK_FLAGS " -Wl,-rpath-link,${LLVM_LIBRARY_OUTPUT_INTDIR} ")
     endif()
   else()
     return()
   endif()
 
-  # Enable BUILD_WITH_INSTALL_RPATH unless CMAKE_BUILD_RPATH is set.
-  if(NOT "${CMAKE_BUILD_RPATH}" STREQUAL "")
-    set_property(TARGET ${name} PROPERTY BUILD_WITH_INSTALL_RPATH ON)
-  endif()
-
   set_target_properties(${name} PROPERTIES
+                        BUILD_WITH_INSTALL_RPATH On
                         INSTALL_RPATH "${_install_rpath}"
                         ${_install_name_dir})
 endfunction()
 
 function(setup_dependency_debugging name)
   if(NOT LLVM_DEPENDENCY_DEBUGGING)
     return()
   endif()