Building latest gpc on Intel OS X 10.5.2

[Peter Schorn]

The problem is solved - I can now successfully build a working gpc 
(cross) compiler on Intel Mac OS X 10.5.2. The following items did the 
trick:

1) A sysctl-free patch for __enable_execute_stack (Thanks to Adriaan and 
  Gale for helping on this one)

2) Using sed 4.1.4. instead of the Apple supplied version of sed (maybe 
it would help to add an sed check in mk-t-inc).

Peter
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peter.schorn at acm.org