scons: Add a pair of functions for working with Value nodes.
scons: Add a pair of functions for working with Value nodes.

These nodes are really for working with text, and they do strange and
broken things otherwise. This change adds a pair of convenience
functions which uses pickle to serialize an object for the Value to
hold, and to unpack the Value later.

Change-Id: Id48822ce3de283b003d4cc7ef6b563a70e321ca6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48371
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Hoa Nguyen <a0aa8449aacb303edcb25d6bbe69da9124f010fc@ucdavis.edu>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>

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