Avoid adding a dep on all headers in ${LOCALBASE}/include, not
compatible with dpb(1) junking.

Index: cmake/modules/LLVMProcessSources.cmake
--- cmake/modules/LLVMProcessSources.cmake.orig
+++ cmake/modules/LLVMProcessSources.cmake
@@ -46,6 +46,9 @@ function(find_all_header_files hdrs_out additional_hea
   list(APPEND all_headers ${hds})
 
   foreach(additional_dir ${additional_headerdirs})
+    if (${additional_dir} MATCHES "^${LOCALBASE}/include")
+      message(FATAL_ERROR "ports: refusing to scan ${additional_dir}")
+    endif()
     add_header_files_for_glob(hds "${additional_dir}/*.h")
     list(APPEND all_headers ${hds})
     add_header_files_for_glob(hds "${additional_dir}/*.inc")