[REG 6.5.0beta3 -> RC] namespace build fails on MSVC2019

cmake -DCMAKE_C_COMPILER=cl.exe -DCMAKE_CXX_COMPILER=cl.exe -GNinja -DCMAKE_BUILD_TYPE=Release -DQT_BUILD_EXAMPLES=OFF -DBUILD_WITH_PCH=OFF -DOPENSSL_ROOT_DIR=C:\openssl\include\.. -DFEATURE_system_zlib=OFF -DPostgreSQL_ROOT=C:\Utils\postgresql\pgsql\lib\.. -DQT_BUILD_TESTS=OFF -DCMAKE_MESSAGE_LOG_LEVEL=STATUS -DQT_NAMESPACE=RTA C:\Users\qt\RTA\src-6.5.0 -DCMAKE_INSTALL_PREFIX:PATH=C:\Users\qt\RTA\src-6.5.0\qtbase 

[354/11183] Building CXX object qtbase\qmake\CMakeFiles\QtLibraryInfo.dir\qmakelibraryinfo.cpp.obj
 FAILED: qtbase/qmake/CMakeFiles/QtLibraryInfo.dir/qmakelibraryinfo.cpp.obj 
C:\PROGRA~2\MICROS~2\2019\PROFES~1\VC\Tools\MSVC\1429~1.301\bin\Hostx64\x64\cl.exe  /nologo /TP -DPROEVALUATOR_FULL -DQMAKE_VERSION_STR=\"3.1\" -DQT_BUILD_QMAKE -DQT_CORE_LIB -DQT_HOST_DATADIR=\".\" -DQT_HOST_MKSPEC=\"win32-msvc\" -DQT_NAMESPACE=RTA -DQT_NO_FOREACH -DQT_TARGET_MKSPEC=\"win32-msvc\" -DQT_USE_QSTRINGBUILDER -DQT_VERSION_STR=\"6.5.0\" -DUNICODE -DWIN32 -DWIN64 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -D_UNICODE -D_WIN64 -IC:\Users\qt\RTA\src-6.5.0\qtbase\src\corelib -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\6.5.0 -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\6.5.0\QtCore -IC:\Users\qt\RTA\src-6.5.0\qtbase\include -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore -IC:\Users\qt\RTA\src-6.5.0\qtbase\mkspecs\win32-msvc -IC:\Users\qt\RTA\src-6.5.0\qtbase\qmake -IC:\Users\qt\RTA\src-6.5.0\qtbase\qmake\library /DWIN32 /D_WINDOWS /DNDEBUG -O2 -MD -Zc:__cplusplus -permissive- -utf-8 -std:c++17 /showIncludes /Foqtbase\qmake\CMakeFiles\QtLibraryInfo.dir\qmakelibraryinfo.cpp.obj /Fdqtbase\qmake\CMakeFiles\QtLibraryInfo.dir\ /FS -c C:\Users\qt\RTA\src-6.5.0\qtbase\qmake\qmakelibraryinfo.cpp
C:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\../../src/corelib/kernel/qvariant.h(54): error C2888: 'const bool qIsRelocatable<RTA::QVariant>': symbol cannot be defined within namespace 'RTA'
[355/11183] Building CXX object qtbase\qmake\CMakeFiles\QtLibraryInfo.dir\property.cpp.obj
 FAILED: qtbase/qmake/CMakeFiles/QtLibraryInfo.dir/property.cpp.obj 
C:\PROGRA~2\MICROS~2\2019\PROFES~1\VC\Tools\MSVC\1429~1.301\bin\Hostx64\x64\cl.exe  /nologo /TP -DPROEVALUATOR_FULL -DQMAKE_VERSION_STR=\"3.1\" -DQT_BUILD_QMAKE -DQT_CORE_LIB -DQT_HOST_DATADIR=\".\" -DQT_HOST_MKSPEC=\"win32-msvc\" -DQT_NAMESPACE=RTA -DQT_NO_FOREACH -DQT_TARGET_MKSPEC=\"win32-msvc\" -DQT_USE_QSTRINGBUILDER -DQT_VERSION_STR=\"6.5.0\" -DUNICODE -DWIN32 -DWIN64 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -D_UNICODE -D_WIN64 -IC:\Users\qt\RTA\src-6.5.0\qtbase\src\corelib -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\6.5.0 -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\6.5.0\QtCore -IC:\Users\qt\RTA\src-6.5.0\qtbase\include -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore -IC:\Users\qt\RTA\src-6.5.0\qtbase\mkspecs\win32-msvc -IC:\Users\qt\RTA\src-6.5.0\qtbase\qmake -IC:\Users\qt\RTA\src-6.5.0\qtbase\qmake\library /DWIN32 /D_WINDOWS /DNDEBUG -O2 -MD -Zc:__cplusplus -permissive- -utf-8 -std:c++17 /showIncludes /Foqtbase\qmake\CMakeFiles\QtLibraryInfo.dir\property.cpp.obj /Fdqtbase\qmake\CMakeFiles\QtLibraryInfo.dir\ /FS -c C:\Users\qt\RTA\src-6.5.0\qtbase\qmake\property.cpp
C:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\../../src/corelib/kernel/qvariant.h(54): error C2888: 'const bool qIsRelocatable<RTA::QVariant>': symbol cannot be defined within namespace 'RTA'
[356/11183] Automatic MOC for target QTlsBackendOpenSSLPlugin
[357/11183] Building CXX object qtbase\qmake\CMakeFiles\QtLibraryInfo.dir\library\proitems.cpp.obj
 FAILED: qtbase/qmake/CMakeFiles/QtLibraryInfo.dir/library/proitems.cpp.obj 
C:\PROGRA~2\MICROS~2\2019\PROFES~1\VC\Tools\MSVC\1429~1.301\bin\Hostx64\x64\cl.exe  /nologo /TP -DPROEVALUATOR_FULL -DQMAKE_VERSION_STR=\"3.1\" -DQT_BUILD_QMAKE -DQT_CORE_LIB -DQT_HOST_DATADIR=\".\" -DQT_HOST_MKSPEC=\"win32-msvc\" -DQT_NAMESPACE=RTA -DQT_NO_FOREACH -DQT_TARGET_MKSPEC=\"win32-msvc\" -DQT_USE_QSTRINGBUILDER -DQT_VERSION_STR=\"6.5.0\" -DUNICODE -DWIN32 -DWIN64 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -D_UNICODE -D_WIN64 -IC:\Users\qt\RTA\src-6.5.0\qtbase\src\corelib -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\6.5.0 -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\6.5.0\QtCore -IC:\Users\qt\RTA\src-6.5.0\qtbase\include -IC:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore -IC:\Users\qt\RTA\src-6.5.0\qtbase\mkspecs\win32-msvc -IC:\Users\qt\RTA\src-6.5.0\qtbase\qmake -IC:\Users\qt\RTA\src-6.5.0\qtbase\qmake\library /DWIN32 /D_WINDOWS /DNDEBUG -O2 -MD -Zc:__cplusplus -permissive- -utf-8 -std:c++17 /showIncludes /Foqtbase\qmake\CMakeFiles\QtLibraryInfo.dir\library\proitems.cpp.obj /Fdqtbase\qmake\CMakeFiles\QtLibraryInfo.dir\ /FS -c C:\Users\qt\RTA\src-6.5.0\qtbase\qmake\library\proitems.cpp
C:\Users\qt\RTA\src-6.5.0\qtbase\include\QtCore\../../src/corelib/kernel/qvariant.h(54): error C2888: 'const bool qIsRelocatable<RTA::QVariant>': symbol cannot be defined within namespace 'RTA'
[358/11183] Automatic MOC for target Core