[c] support dynamic loading on Windows: test

Author: jll63

test/dynamic_loading/CMakeLists.txt

@@ -32,6 +32,11 @@ target_link_libraries(
 # ENABLE_EXPORTS is required so that symbols from each shared library are
 # visible to other shared libraries loaded at runtime (e.g. dl_test_overrider
 # can resolve symbols from dl_test_method/dl_test_registry).
+# CXX_VISIBILITY_PRESET must be "default" so that the template static variables
+# used as the shared registry state (policy statics) are exported with DEFAULT
+# ELF visibility. With hidden visibility (as set by BoostRoot.cmake in the
+# super-project build) they become UNIQUE HIDDEN and are not deduplicated by
+# the dynamic linker, breaking cross-DSO state sharing.
 foreach(
     target dl_test_registry dl_test_method dl_test_overrider
            boost_openmethod-test_dynamic_loading)
@@ -41,7 +46,9 @@ foreach(
             RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
             LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
             ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
-            ENABLE_EXPORTS ON)
+            ENABLE_EXPORTS ON
+            CXX_VISIBILITY_PRESET default
+            VISIBILITY_INLINES_HIDDEN OFF)
 endforeach()
 
 add_test(