Remove redundant CMake loop. (#12779)

diff --git a/build_tools/cmake/iree_compiler_plugin.cmake b/build_tools/cmake/iree_compiler_plugin.cmake
index efeec70..1dad633 100644
--- a/build_tools/cmake/iree_compiler_plugin.cmake
+++ b/build_tools/cmake/iree_compiler_plugin.cmake
@@ -47,16 +47,7 @@
 
   # Generate an include() in compiler/plugins/CMakeLists.txt for each plugin dir.
   set(_contents)
-  foreach(_d ${IREE_COMPILER_BUILTIN_PLUGIN_PATHS})
-    cmake_path(ABSOLUTE_PATH _d BASE_DIRECTORY "${IREE_SOURCE_DIR}" NORMALIZE)
-    set(_f "${_d}/iree_compiler_plugin_group.cmake")
-    if(NOT EXISTS "${_f}")
-      message(SEND_ERROR "Specified plugin directory ${_d} does not contain an iree_compiler_plugin_group.cmake file")
-      continue()
-    endif()
-    string(APPEND _contents "include(${_f})\n")
-  endforeach()
-  foreach(_d ${IREE_COMPILER_PLUGIN_PATHS})
+  foreach(_d ${IREE_COMPILER_BUILTIN_PLUGIN_PATHS} ${IREE_COMPILER_PLUGIN_PATHS})
     cmake_path(ABSOLUTE_PATH _d BASE_DIRECTORY "${IREE_SOURCE_DIR}" NORMALIZE)
     set(_f "${_d}/iree_compiler_plugin_group.cmake")
     if(NOT EXISTS "${_f}")