aco: Use unreachable instead assert(false)

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18194>

src/amd/compiler/aco_opt_value_numbering.cpp

@@ -278,7 +278,7 @@ struct InstrPred {
       case Format::EXP:
       case Format::SOPP:
       case Format::PSEUDO_BRANCH:
-      case Format::PSEUDO_BARRIER: assert(false);
+      case Format::PSEUDO_BARRIER: unreachable("unsupported instruction format");
       default: return true;
       }
    }