Don't call export_symbols.py with duplicate libs

Summary:
export_symbols.py discards duplicate symbols, assuming they have public definitions, so if we end
up calling it with duplicate libraries we will end up with an inaccurate export list.

Reviewers: jasonliu, stevewan, john.brawn

Reviewed By: john.brawn

Subscribers: mgorny, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70918

Author: daltenty

llvm/cmake/modules/AddLLVM.cmake

@@ -873,6 +873,7 @@ function(export_executable_symbols target)
       set(new_libs ${newer_libs})
       set(newer_libs "")
     endwhile()
+    list(REMOVE_DUPLICATES static_libs)
     if (MSVC)
       set(mangling microsoft)
     else()