llvm-shlib: Fix libLLVM-${MAJOR}.so symlink on MacOS (llvm#85163)

This is a partial revert of 10c48a7
with a fix for the symlink target name on MacOS

See llvm#84637

(cherry picked from commit ec2b752)

Author: tstellar

llvm/cmake/modules/AddLLVM.cmake

@@ -2074,7 +2074,7 @@ function(add_lit_testsuites project directory)
 endfunction()
 
 function(llvm_install_library_symlink name dest type)
-  cmake_parse_arguments(ARG "" "COMPONENT;SOVERSION" "" ${ARGN})
+  cmake_parse_arguments(ARG "FULL_DEST" "COMPONENT" "" ${ARGN})
   foreach(path ${CMAKE_MODULE_PATH})
     if(EXISTS ${path}/LLVMInstallSymlink.cmake)
       set(INSTALL_SYMLINK ${path}/LLVMInstallSymlink.cmake)
@@ -2088,8 +2088,8 @@ function(llvm_install_library_symlink name dest type)
   endif()
 
   set(full_name ${CMAKE_${type}_LIBRARY_PREFIX}${name}${CMAKE_${type}_LIBRARY_SUFFIX})
-  if (ARG_SOVERSION)
-    set(full_dest ${CMAKE_${type}_LIBRARY_PREFIX}${dest}${CMAKE_${type}_LIBRARY_SUFFIX}.${ARG_SOVERSION})
+  if (ARG_FULL_DEST)
+    set(full_dest ${dest})
   else()
     set(full_dest ${CMAKE_${type}_LIBRARY_PREFIX}${dest}${CMAKE_${type}_LIBRARY_SUFFIX})
   endif()

llvm/tools/llvm-shlib/CMakeLists.txt

@@ -35,8 +35,7 @@ if(LLVM_BUILD_LLVM_DYLIB)
   endif()
   add_llvm_library(LLVM SHARED DISABLE_LLVM_LINK_LLVM_DYLIB OUTPUT_NAME LLVM ${INSTALL_WITH_TOOLCHAIN} ${SOURCES})
   # Add symlink for backwards compatibility with old library name
-  get_target_property(LLVM_DYLIB_SOVERSION LLVM SOVERSION)
-  llvm_install_library_symlink(LLVM-${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX} LLVM SHARED COMPONENT LLVM SOVERSION ${LLVM_DYLIB_SOVERSION})
+  llvm_install_library_symlink(LLVM-${LLVM_VERSION_MAJOR}${LLVM_VERSION_SUFFIX} $<TARGET_SONAME_FILE_NAME:LLVM> SHARED FULL_DEST COMPONENT LLVM)
 
   list(REMOVE_DUPLICATES LIB_NAMES)
   if("${CMAKE_SYSTEM_NAME}" STREQUAL "Darwin")