genautomata fix

[Bernd Schmidt <bernds at codesourcery dot com>]

This fixes a problem I found in genautomata while working on a new port.
 If you have extra parentheses in a regexp, e.g. "(s1)+s1w", we
construct a copy of the string "r1" in alloca'd memory on the stack.
Later, a pointer to that can escape because when there's only one
element in a string, we use the original string rather than the copy we
made on an obstack.

The extra parentheses are there because the scheduling description is
semi-generated and the input expression can expand to "(s1+x1)+s1w" in
other cases.

Fixed with this patch.  Bootstrapped and regression tested on
i686-linux.  Ok?


Bernd

Attachment: ga-alloca.diff
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