qtdoc fails to build with an assertion failure in libclang on i586

When building qtdoc on i586, the build fails with:

/home/abuild/rpmbuild/BUILD/qt-everywhere-src-5.11.0-rc/qtbase/src/corelib/qdoc_wrapper.sh -outputdir /home/abuild/rpmbuild/BUILD/qt-everywhere-src-5.11.0-rc/qtbase/doc/qtcore -installdir /usr/share/doc/packages/qt5 /home/abuild/rpmbuild/BUILD/qt-everywhere-src-5.11.0-rc/qtbase/src/corelib/doc/qtcore.qdocconf -prepare -no-link-errors -I. -Iglobal -I../3rdparty/harfbuzz/src -I../3rdparty/md5 -I../3rdparty/md4 -I../3rdparty/sha3 -I../3rdparty/forkfd -I../../include -I../../include/QtCore -I../../include/QtCore/5.11.0 -I../../include/QtCore/5.11.0/QtCore -I.moc -I.tracegen -isystem /usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I../../mkspecs/linux-g++
[ 348s] QT_HASH_SEED: forced seed value is not 0, cannot guarantee that the hashing functions will produce a stable value.qdoc: ../tools/clang/lib/Serialization/ASTWriter.cpp:4046: void clang::ASTWriter::GenerateNameLookupTable(const clang::DeclContext *, llvm::SmallVectorImpl<char>&): Assertion `ConversionNameSet.empty() && "Failed to find all of the visible " "conversion functions by walking all " "the lexical members of the context."' failed.
[ 348s] libclang: crash detected during AST saving:

Unknown macro: { [ 348s] 'filename' }

[ 348s] qdoc: ../include/llvm/Bitcode/BitstreamWriter.h:90: llvm::BitstreamWriter::~BitstreamWriter(): Assertion `BlockScope.empty() && CurAbbrevs.empty() && "Block imbalance"' failed.

This was previously reported at: https://bugzilla.opensuse.org/show_bug.cgi?id=1092425