CUDA: Add per-language module -DEF: flag on Windows

NVIDIA CUDA links with `link.exe` directly, but had no
`CMAKE_CUDA_LINK_DEF_FILE_FLAG` and fell back to the global
`CMAKE_LINK_DEF_FILE_FLAG`.  With IntelLLVM enabled in the same build
tree, that holds `/Qoption,link,/DEF:`, which `link.exe` ignores, so a
CUDA DLL exported nothing from its `.def` file.  Commit 8b710d8264
(Linker: Generate per-language module -DEF: flags on Windows,
2025-05-28) covered the other Windows toolchains but missed CUDA.

Fixes: #25598
Issue: #26005

Modules/Platform/Windows-NVIDIA-CUDA.cmake

@@ -26,6 +26,7 @@ set(CMAKE_CUDA_SHARED_LIBRARY_COMPILE_DEFINITIONS "_WINDLL")
 set(CMAKE_CUDA_CREATE_SHARED_MODULE ${CMAKE_CUDA_CREATE_SHARED_LIBRARY})
 set(CMAKE_CUDA_CREATE_STATIC_LIBRARY  "<CMAKE_AR> ${CMAKE_CL_NOLOGO}${_PLATFORM_ARCHIVE_FLAGS} <LINK_FLAGS> /out:<TARGET> <OBJECTS> ")
 set(CMAKE_CUDA_LINKER_SUPPORTS_PDB ON)
+set(CMAKE_CUDA_LINK_DEF_FILE_FLAG "/DEF:")
 set(CMAKE_CUDA_LIBRARY_PATH_FLAG "-LIBPATH:")
 set(CMAKE_CUDA_LINK_EXECUTABLE
   "${_CMAKE_VS_LINK_EXE}<CMAKE_LINKER> ${CMAKE_CL_NOLOGO} <OBJECTS> ${CMAKE_START_TEMP_FILE} /out:<TARGET> /implib:<TARGET_IMPLIB> /pdb:<TARGET_PDB> /version:<TARGET_VERSION_MAJOR>.<TARGET_VERSION_MINOR>${_PLATFORM_LINK_FLAGS} <LINK_FLAGS> <LINK_LIBRARIES>${__IMPLICIT_LINKS} ${CMAKE_END_TEMP_FILE}")

Tests/CudaOnly/CMakeLists.txt

@@ -12,6 +12,7 @@ add_cuda_test_macro(CudaOnly.CompileFlags CudaOnlyCompileFlags)
 add_cuda_test_macro(CudaOnly.EnableStandard CudaOnlyEnableStandard)
 add_cuda_test_macro(CudaOnly.ExportPTX CudaOnlyExportPTX)
 add_cuda_test_macro(CudaOnly.LinkDirectory CudaOnlyLinkDirectory)
+add_cuda_test_macro(CudaOnly.ModuleDefinition CudaOnlyModuleDefinition)
 add_cuda_test_macro(CudaOnly.SharedRuntimePlusToolkit CudaOnlySharedRuntimePlusToolkit)
 add_cuda_test_macro(CudaOnly.StaticRuntimePlusToolkit CudaOnlyStaticRuntimePlusToolkit)
 if(NOT WIN32 AND CMake_TEST_CUDA STREQUAL "NVIDIA")

Tests/CudaOnly/ModuleDefinition/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.18)
+project(ModuleDefinition CUDA)
+
+if(MSVC)
+  # Simulate another language overriding the -DEF: flag.
+  # The generators prefer CMAKE_<LANG>_LINK_DEF_FILE_FLAG.
+  set(CMAKE_LINK_DEF_FILE_FLAG "bad-def-flag:")
+endif()
+
+# Symbols are exported only through the .def file.
+add_library(CudaOnlyModuleDefinitionLib SHARED lib.cu lib.def)
+
+add_executable(CudaOnlyModuleDefinition main.cu)
+target_link_libraries(CudaOnlyModuleDefinition PRIVATE CudaOnlyModuleDefinitionLib)

Tests/CudaOnly/ModuleDefinition/lib.cu

@@ -0,0 +1,4 @@
+extern "C" int moddef_answer()
+{
+  return 42;
+}

Tests/CudaOnly/ModuleDefinition/lib.def

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

Tests/CudaOnly/ModuleDefinition/main.cu

@@ -0,0 +1,6 @@
+extern "C" int moddef_answer();
+
+int main()
+{
+  return moddef_answer() == 42 ? 0 : 1;
+}