gfortran patch for PR28974 Slow compilation of data statements.

[Jerry DeLisle]

:REVIEWMAIL:
Bud Davis wrote:
> The below patch uses a splay tree instead of a linked
> list for accessing constructors by offset (index).
> 
> In order to keep from changing about 50% of the
> routines in the front end, i kept the existing linked
> list representation intact; so when needed a splay
> tree is used in addition to the linked list.
> 

While working pr24978, I have studied this section of code quite a bit and I 
understand most of it.   I would say this patch is OK for trunk unless someone 
else chimes in.

Jerry