message: Add a comment explaining part of the build script
diff: @@ -304,6 +304,9 @@ def build(bld):
  lib.append('ncurses')
  if bld.env['use_system_clang']:
  + # If the user passed `--llvm-config=` (setting `llvm-config` to
  + # the empty string) to the configure phase, we should not try to
  + # run it.
  if bld.env['llvm_config']:
  rpath = str(subprocess.check_output(
  [bld.env['llvm_config'], '--libdir'],
  