Build failure with GCC-15

[orlitzky]

We've started build testing everything with the pre-release versions of gcc-15 to get a head start on the breakage. This one looks new:

In file included from ../src/kernel/recint/rdiv.h:48,
                 from ../src/kernel/recint/rint.h:53,
                 from test-rint_arith.C:17:
../src/kernel/recint/rfiddling.h: In static member function ‘static RecInt::rint<K> RecInt::rint<K>::maxFFLAS()’:
../src/kernel/recint/rfiddling.h:170:29: error: ‘class RecInt::rint<K>’ has no member named ‘Low’ [-Wtemplate-body[https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html#index-Wno-template-body]]
  170 |         set_highest_bit(max.Low.Value);
      |                             ^~~

The full build log was posted to our bug tracker at https://bugs.gentoo.org/939096