Merge bitcoin#26823: refactor: Work around Werror=free-nonheap-object…

… in AssumeCalculateMemPoolAncestors

faa86ee refactor: Work around Werror=free-nonheap-object in AssumeCalculateMemPoolAncestors (MarcoFalke)

Pull request description:

  This works around the s390x gcc bug mentioned in bitcoin#26820

ACKs for top commit:
  achow101:
    ACK faa86ee

Tree-SHA512: 041d5daa157ea1856b0a8027181085d70624f5f8822049ace9963e90c653bbb8c91d1f16b8a5bf460687eb4ed13f1db72e3885a511aadbad6dede93d9f9ccd6d

src/txmempool.cpp

@@ -260,8 +260,8 @@ CTxMemPool::setEntries CTxMemPool::AssumeCalculateMemPoolAncestors(
     const Limits& limits,
     bool fSearchForParents /* = true */) const
 {
-    auto result{Assume(CalculateMemPoolAncestors(entry, limits, fSearchForParents))};
-    if (!result) {
+    auto result{CalculateMemPoolAncestors(entry, limits, fSearchForParents)};
+    if (!Assume(result)) {
         LogPrintLevel(BCLog::MEMPOOL, BCLog::Level::Error, "%s: CalculateMemPoolAncestors failed unexpectedly, continuing with empty ancestor set (%s)\n",
                       calling_fn_name, util::ErrorString(result).original);
     }