base: Avoid an unused expression error in GEM5_DEPRECATED_MACRO.
base: Avoid an unused expression error in GEM5_DEPRECATED_MACRO.

If the lambda in that macro is not actually called, clang complains
about an unused expression which breaks the build.

Change-Id: Id8708944cbac4c937e833583da0c2c18422230c0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45719
Reviewed-by: Daniel Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5