[clang] [lldb] [llvm] [cmake] Build executables with -no_exported_symbols when building Apple toolchain (PR #87684)

[Dan Liew via cfe-commits]

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@@ -258,15 +258,24 @@ if (NOT DEFINED LLVM_LINKER_DETECTED AND NOT WIN32)
     endif()
   endif()
 
-  # Apple's linker complains about duplicate libraries, which CMake likes to do
-  # to support ELF platforms. To silence that warning, we can use
-  # -no_warn_duplicate_libraries, but only in versions of the linker that
-  # support that flag.
-  if(NOT LLVM_USE_LINKER AND ${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+  if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
     include(CheckLinkerFlag)
-    check_linker_flag(C "-Wl,-no_warn_duplicate_libraries" LLVM_LINKER_SUPPORTS_NO_WARN_DUPLICATE_LIBRARIES)
-  else()
-    set(LLVM_LINKER_SUPPORTS_NO_WARN_DUPLICATE_LIBRARIES OFF CACHE INTERNAL "")
+    # Linkers that support Darwin allow a setting to internalize all symbol exports, 
+    # aiding in reducing binary size and often is applicable for executables.
+    check_linker_flag(C "-Wl,-no_exported_symbols" LLVM_LINKER_SUPPORTS_NO_EXPORTED_SYMBOLS)
+    
+    if (NOT LLVM_USE_LINKER) 
+      # Apple's linker complains about duplicate libraries, which CMake likes to do
+      # to support ELF platforms. To silence that warning, we can use
+      # -no_warn_duplicate_libraries, but only in versions of the linker that
+      # support that flag.
+      check_linker_flag(C "-Wl,-no_warn_duplicate_libraries" LLVM_LINKER_SUPPORTS_NO_WARN_DUPLICATE_LIBRARIES)
+    else()
+      set(LLVM_LINKER_SUPPORTS_NO_WARN_DUPLICATE_LIBRARIES OFF CACHE INTERNAL "")
----------------
delcypher wrote:

Nit: This won't do anything if `LLVM_LINKER_SUPPORTS_NO_WARN_DUPLICATE_LIBRARIES` is already set in the cache (e.g. from a previous configure). You can use `FORCE` to always set the value.

https://github.com/llvm/llvm-project/pull/87684