qtserialbus many compile errors

Linux g++ v10.1

I know qtserialbus will be going away soon, since both the serial and parallel ports are replaced by USB3, but meantime, git clone as of this date fails to compile.

qt5/qtserialbus/src/serialbus/qmodbusclient_p.h missing '#include <climits>': line 45 refers to INT_MIN which is defined in climits.

qt5/qtserialbus/src/serialbus/qmodbuspdu.cpp:442:89: warning: ‘constexpr QChar::QChar(char)’ is deprecated: Use fromUtf8, QStringLiteral, or QLatin1String [-Wdeprecated-declarations]

qt5/qtserialbus/src/serialbus/qmodbustcpclient_p.h:90:93: error: no matching function for call to ‘QOverload<QAbstractSocket::SocketError>::of(QAbstractSocket::SocketError(QAbstractSocket::*)() const)’

qt5/build/qtbase/include/QtCore/../../../../qtbase/src/corelib/global/qglobal.h:1216:34: note: candidate: ‘template<class R, class T> static constexpr decltype (ptr) QNonConstOverload<Args>::of(R (T::*)(Args ...)) [with R = R; T = T; Args = \{QAbstractSocket::SocketError}]’

note: template argument deduction/substitution failed:
In file included from qt5/qtserialbus/src/serialbus/qmodbustcpclient.cpp:38:
qt5/qtserialbus/src/serialbus/qmodbustcpclient_p.h:90:93: note: types‘R (T:(QAbstractSocket::SocketError)’ and ‘QAbstractSocket::SocketError (QAbstractSocket:() const’ have incompatible cv-qualifiers
QOverload<QAbstractSocket::SocketError>::of(&QAbstractSocket::error)