[test][static-stdlib] Test with swift_static when building only static stdlib

This patch makes the test suite use `lib/swift_static` instead of
`lib/swift` when building only static stdlib.

Author: kateinoigakukun

test/CMakeLists.txt

@@ -155,8 +155,14 @@ if(NOT SWIFT_INCLUDE_TOOLS)
       )
   endif()
   if(SWIFT_BUILD_STDLIB)
-    list(APPEND SWIFT_LIT_ARGS
-         "--param" "test_resource_dir=${SWIFTLIB_DIR}")
+    # if building only static stdlib, prefer static lib.
+    if(NOT SWIFT_BUILD_DYNAMIC_STDLIB AND SWIFT_BUILD_STATIC_STDLIB)
+      list(APPEND SWIFT_LIT_ARGS
+           "--param" "test_resource_dir=${SWIFTSTATICLIB_DIR}")
+    else()
+      list(APPEND SWIFT_LIT_ARGS
+           "--param" "test_resource_dir=${SWIFTLIB_DIR}")
+    endif()
   endif()
 endif()