Support WINDOWS_EXPORT_ALL_SYMBOLS with .def files

The `WINDOWS_EXPORT_ALL_SYMBOLS` target property exports all symbols
found in object files explicitly given to the linker.  However, the
linker may also find additional symbols in dependencies and copy them
into the linked binary (e.g. from `msvcrt.lib`).  Provide a way to
export an explicit list of such symbols by adding a `.def` file as a
source file.

Fixes: #16473

Tests/ModuleDefinition/CMakeLists.txt

@@ -4,6 +4,8 @@ project(ModuleDefinition C)
 # Test .def file source recognition for DLLs.
 add_library(example_dll SHARED example_dll.c example_dll.def)
 
+add_library(split_dll SHARED split_dll.c split_dll_1.def split_dll_2.def)
+
 # Test generated .def file.
 add_custom_command(OUTPUT example_dll_gen.def
   DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/example_dll_gen.def.in
@@ -24,7 +26,12 @@ endif()
 # Test .def file source recognition for EXEs.
 add_executable(example_exe example_exe.c example_exe.def)
 set_property(TARGET example_exe PROPERTY ENABLE_EXPORTS 1)
-target_link_libraries(example_exe example_dll example_dll_gen ${example_dll_2})
+target_link_libraries(example_exe
+  example_dll
+  example_dll_gen
+  ${example_dll_2}
+  split_dll
+  )
 
 # Test linking to the executable.
 add_library(example_mod_1 MODULE example_mod_1.c)

Tests/ModuleDefinition/example_exe.c

@@ -3,15 +3,19 @@ extern int __declspec(dllimport) example_dll_gen_function(void);
 #ifdef EXAMPLE_DLL_2
 extern int __declspec(dllimport) example_dll_2_function(void);
 #endif
+extern int __declspec(dllimport) split_dll_1(void);
+extern int __declspec(dllimport) split_dll_2(void);
+
 int example_exe_function(void)
 {
   return 0;
 }
+
 int main(void)
 {
   return example_dll_function() + example_dll_gen_function() +
 #ifdef EXAMPLE_DLL_2
     example_dll_2_function() +
 #endif
-    example_exe_function();
+    split_dll_1() + split_dll_2() + example_exe_function();
 }

Tests/ModuleDefinition/split_dll.c

@@ -0,0 +1,9 @@
+int split_dll_1(void)
+{
+  return 0;
+}
+
+int split_dll_2(void)
+{
+  return 0;
+}

Tests/ModuleDefinition/split_dll_1.def

@@ -0,0 +1,2 @@
+EXPORTS
+split_dll_1

Tests/ModuleDefinition/split_dll_2.def

@@ -0,0 +1,2 @@
+EXPORTS
+split_dll_2