dll_index NO_COPY patch

[Jason Tishler <jason at tishler dot net>]

The attached patch fixes the problem described in the following thread:

    http://cygwin.com/ml/cygwin-developers/2002-11/msg00019.html

Given the following facts:

    1. During fork(), fork_copy() is run after
       dll_list::load_after_fork().
    2. The static dll_index variable in include/cygwin/cygwin_dll.h is
       not marked NO_COPY.
    3. The dll structure allocated by dll_list::alloc() is not
       guaranteed to be the same in the parent and child.

I believe that the following is the correct root cause analysis of the
problem:

    When #3 above occurs, fork_copy() overwrites the child's dll_index
    with the parent's value.  This causes dll_list::detach() to access
    unallocated memory which in turn causes the child to stackdump.

Jason

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