Emscripten: Enable de-duplication of libraries for CMP0156 with LLD

LLD automatically resolves newly encountered symbols using object files
previously encountered.  Also, the Emscripten compiler driver invokes
the LLD linker with `--whole-archive ... --no-whole-archive` around all
the libraries.  Therefore we should not repeat any.

Issue: #27232
Suggested-by: Marc Chevrier <marc.chevrier@gmail.com>

Modules/Platform/Linker/Emscripten-LLD.cmake

@@ -8,4 +8,7 @@ macro(__emscripten_linker_lld lang)
   set(CMAKE_${lang}_LINK_LIBRARY_USING_WHOLE_ARCHIVE "-Wl,--whole-archive" "<LINK_ITEM>" "-Wl,--no-whole-archive")
   set(CMAKE_${lang}_LINK_LIBRARY_USING_WHOLE_ARCHIVE_SUPPORTED TRUE)
   set(CMAKE_${lang}_LINK_LIBRARY_WHOLE_ARCHIVE_ATTRIBUTES LIBRARY_TYPE=STATIC DEDUPLICATION=YES OVERRIDE=DEFAULT)
+
+  set(CMAKE_${lang}_PLATFORM_LINKER_ID LLD)
+  set(CMAKE_${lang}_LINK_LIBRARIES_PROCESSING ORDER=REVERSE DEDUPLICATION=ALL)
 endmacro()

Tests/RunCMake/Emscripten/C-lib-circular.cmake

@@ -0,0 +1,10 @@
+enable_language(C)
+
+add_library(circular1 STATIC circular1.c)
+add_library(circular2 STATIC circular2.c)
+
+target_link_libraries(circular1 PRIVATE circular2)
+target_link_libraries(circular2 PRIVATE circular1)
+
+add_executable(main_circular main_circular.c)
+target_link_libraries(main_circular PRIVATE circular1)

Tests/RunCMake/Emscripten/RunCMakeTest.cmake

@@ -63,6 +63,11 @@ foreach(_emscripten_toolchain IN LISTS _emscripten_toolchains)
     -DCMAKE_C_COMPILER=${c_comp}
   )
 
+  run_toolchain(C-lib-circular
+    -DCMAKE_SYSTEM_NAME=Emscripten
+    -DCMAKE_C_COMPILER=${c_comp}
+  )
+
   run_cmake_with_options(C-WHOLE_ARCHIVE
     -DCMAKE_SYSTEM_NAME=Emscripten
     -DCMAKE_C_COMPILER=${c_comp}