Don't set LLVM_NO_DEAD_STRIP on AIX

[daltenty]

Summary

when building plugins, as AIX has symbols in it's standard library that
must be garbage collected or we will see link errors. Export lists will
handle this instead on AIX.

[DiggerLin]

LGTM

llvm/cmake/modules/AddLLVM.cmake

if(DEFINED windows_resource_file)
     set_windows_version_resource_properties(${name} ${windows_resource_file})
   endif()
 
   # $<TARGET_OBJECTS> doesn't require compile flags.
   if(NOT LLVM_ENABLE_OBJLIB)
     llvm_update_compile_flags(${name})
   endif()
 
-  if (ARG_SUPPORT_PLUGINS)
+  if (ARG_SUPPORT_PLUGINS AND NOT ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
     set(LLVM_NO_DEAD_STRIP On)
   endif()
 
   add_link_opts( ${name} )
 
   # Do not add -Dname_EXPORTS to the command-line when building files in this
   # target. Doing so is actively harmful for the modules build because it
   # creates extra module variants, and not useful because we don't use these