Generate a .pe script for one design size at a time. (issue 102760043)

[hanwenn]

Reviewers: J_lowe, lemzwerg,

Message:
2nd try ...

Description:
Generate a .pe script for one design size at a time.

In make

 a b: c
   command

is shorthand for

 a: c
   command
 b: c
   command

this means that in parallel builds the same command may be invoked
twice.

Fix this by associating each command with only one target, and adding
dummy dependencies. Also, generate the .pe for only one design size at
a time.

Relative to botched commit 366316fd6be846c2050be6b1b3955b261026187e,
this:

* does not write .dep files from gen-emmentaler-scripts (the makefile
  already writes them)

* declares explicit dependencies on out/*.lisp for the out/%.otf-table
  rule.

Please review this at https://codereview.appspot.com/102760043/

Affected files (+55, -82 lines):
  M mf/GNUmakefile
  M scripts/build/gen-emmentaler-scripts.py