Bug#1097952: superlu-dist: ftbfs with GCC-15

[Drew Parsons]

Source: superlu-dist
Followup-For: Bug #1097952
Control: severity -1 important
Control: tags -1 fixed-upstream
Control: forwarded -1 https://github.com/xiaoyeli/superlu_dist/pull/185

This issue has a patch upstream, but updating is block by the CombBLAS
problem in Bug#1103651.

In the meantime the build flag workaround in 8.2.1+dfsg1-5.1 keeps the
package running, so I'm downgrading severity.

Drew