reproducible builds of *.a static libaries

[Alexander Couzens]

Hi,

while working on reproducible builds [1], I've noticed ncurses is not
reproducible, when creating *.a.
 
While looking further into the problem, I've found aclocal.m4 is
checking if the "ar" support "-curvU". The U stands for
non-deterministic. 

I don't know the reason or history for the -D, I've attached a patch
to change this to D which is deterministic.
It would be also possible to remove the D or U flags completely. "ar"
would then fallback to it's own default, which is on some distribution
deterministic.

Best Regards,
lynxis

[1] https://reproducible-builds.org
-- 
Alexander Couzens

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fix-reproducible.patch
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