The following patch makes some cosmetic changes to m4 macros in pkg.m4.

1) ifelse([$7], [], [this], [$7]) is the same as m4_default([$7], [this])

2) Whitespace before each m4 parameter is ignored, so the`dnl' in the folowing is redundant:
  MACRO(dnl
  parameter)

3) Shell syntax does not allow empty command the `then' or `else' branch; that's why you can see things like:
  if test $foo = yes; then
     ifelse([$3], , :, [$3])
  fi
But if the possible empty $3 is not alone there, no magic is needed:
  if test $foo = yes; then
     echo Oh, yes!
     $3
  fi