fix '-Wunused' warning in ieee.numeric_std

[kammoh]

Just to get rid of the superfluous warning which pops up in every elaboration, when using -Wunused warning switch and VHDL < 2008.

../../src/ieee/v93/numeric_std-body.vhdl:2373:14:warning: variable "value" is never referenced [-Wunused]

Description Please explain the changes you made here.
If the feature changes current behaviour, explain why your solution is better.

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[tgingold]

Wait, do you have a simple testcase ? Warnings are supposed to be disabled for any external units. OTOH, this is a real cleanup.

[inkdot7]

Perhaps this commit could be rebased onto current master, to see if the tests are ok?
(I'm seeing the same and a few more warnings about unused, so would be nice to solve this.)

[tgingold]

Do you have a testcase that shows this warning ?

[inkdot7]

When running with docker image ghdl/vunit:gcc, the following

a.vhd.txt
build.sh.txt

gives

err.txt

[tgingold]

Thank you for the reproducer. I am testing a fix.