std::stable_sort() where libc++ debug mode breaks a unittest

Libc++ debug has a feature that randomizes equal elements during
sort, which normally wouldn't make a difference, but some tests
rely on specific order of tested data. The ones failing without
this include:
CppunitTest_sw_ooxmlexport testMsoPosition
CppunitTest_sw_xhtmlexport testTdf66305
CppunitTest_sw_ww8export testCommentExport

Change-Id: Id49846939a264150cc82091718ffe6b904d7130e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/134337
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

svl/source/items/stylepool.cxx

@@ -261,7 +261,7 @@ namespace {
             // Sort the parents using their name, if they have one.
             if (!rParentNames.empty())
             {
-                std::sort(maParents.begin(), maParents.end(),
+                std::stable_sort(maParents.begin(), maParents.end(),
                           [&rParentNames](const SfxItemSet* pA, const SfxItemSet* pB) {
                               OUString aA;
                               OUString aB;

sw/source/filter/ww8/writerhelper.cxx

@@ -838,7 +838,7 @@ namespace sw
 
         RedlineStack::~RedlineStack()
         {
-            std::sort(maStack.begin(), maStack.end(), CompareRedlines());
+            std::stable_sort(maStack.begin(), maStack.end(), CompareRedlines());
             std::for_each(maStack.begin(), maStack.end(), SetInDocAndDelete(mrDoc));
         }
 

sw/source/filter/ww8/wrtw8nds.cxx

@@ -220,7 +220,7 @@ SwWW8AttrIter::SwWW8AttrIter(MSWordExportBase& rWr, const SwTextNode& rTextNd) :
      Get list of any graphics which may be anchored from this paragraph.
     */
     maFlyFrames = GetFramesInNode(rWr.m_aFrames, m_rNode);
-    std::sort(maFlyFrames.begin(), maFlyFrames.end(), sortswflys());
+    std::stable_sort(maFlyFrames.begin(), maFlyFrames.end(), sortswflys());
 
     /*
      #i18480#