build: resolve 32 bit compilation failure

[javacruft]

Ensure same type comparison (size_t) on 32 bit architectures,
resolving compilation failure:

In file included from /<<PKGBUILDDIR>>/libtcmu.h:24,
                 from /<<PKGBUILDDIR>>/tcmur_cmd_handler.c:20:
/<<PKGBUILDDIR>>/tcmur_cmd_handler.c: In function ‘handle_writesame’:
/<<PKGBUILDDIR>>/libtcmu_common.h:82:14: error: comparison of distinct pointer types lacks a cast [-Werror]
   82 |  (void) (&_a == &_b);  \
      |              ^~
/<<PKGBUILDDIR>>/tcmur_cmd_handler.c:728:11: note: in expansion of macro ‘min’
  728 |  length = min(length, tcmu_lba_to_byte(dev, lba_cnt));
      |

when "-Werror" is enabled by the compiler.