Fix build error when SLANG_ENABLE_TESTS is set to OFF

When SLANG_ENABLE_TESTS is disabled but SLANG_ENABLE_GFX is enabled,
cmake was failing. It turned out that gfx build target was trying to
copy some of files to the directory where slang-test uses. When
SLANG_ENABLE_TESTS is disabled, the directory information became
unavailable, because slang-test target became unavailable.

This commit makes the copying behavior conditional on SLANG_ENABLE_TESTS
in the gfx build target.

Author: jkwak-work

tools/CMakeLists.txt

@@ -156,29 +156,31 @@ if(SLANG_ENABLE_GFX)
             ${slang_SOURCE_DIR}
             ${slang_SOURCE_DIR}/include
         INCLUDE_DIRECTORIES_PRIVATE ${NVAPI_INCLUDE_DIRS}
-        REQUIRES copy-gfx-slang-modules
         INSTALL
         EXPORT_SET_NAME SlangTargets
         FOLDER gfx
     )
-    set(modules_dest_dir $<TARGET_FILE_DIR:slang-test>)
-    add_custom_target(
-        copy-gfx-slang-modules
-        COMMAND ${CMAKE_COMMAND} -E make_directory ${modules_dest_dir}
-        COMMAND
-            ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_LIST_DIR}/gfx/gfx.slang
-            ${modules_dest_dir}/gfx.slang
-        COMMAND
-            ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_LIST_DIR}/gfx/slang.slang
-            ${modules_dest_dir}/slang.slang
-        WORKING_DIRECTORY ${slang_SOURCE_DIR}
-        VERBATIM
-    )
-    set_target_properties(copy-gfx-slang-modules PROPERTIES FOLDER generators)
-    install(
-        FILES ${modules_dest_dir}/gfx.slang ${modules_dest_dir}/slang.slang
-        DESTINATION ${runtime_subdir}
-    )
+    if(SLANG_ENABLE_TESTS)
+        set(modules_dest_dir $<TARGET_FILE_DIR:slang-test>)
+        add_custom_target(
+            copy-gfx-slang-modules
+            COMMAND ${CMAKE_COMMAND} -E make_directory ${modules_dest_dir}
+            COMMAND
+                ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_LIST_DIR}/gfx/gfx.slang
+                ${modules_dest_dir}/gfx.slang
+            COMMAND
+                ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_LIST_DIR}/gfx/slang.slang
+                ${modules_dest_dir}/slang.slang
+            WORKING_DIRECTORY ${slang_SOURCE_DIR}
+            VERBATIM
+        )
+        set_target_properties(copy-gfx-slang-modules PROPERTIES FOLDER generators)
+        install(
+            FILES ${modules_dest_dir}/gfx.slang ${modules_dest_dir}/slang.slang
+            DESTINATION ${runtime_subdir}
+        )
+        add_dependencies(gfx copy-gfx-slang-modules)
+    endif()
 
     slang_add_target(
         gfx-util