Same error as someone else also reported on the blog:
http://grulja.wordpress.com/2014/08/07/plasma-nm-0-9-3-4-is-out/

In file included from /var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:24:0:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:22: error: 'QTextStream' has not been declared
     QString saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName);
                      ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp: In member function 'virtual NMVariantMapMap OpenVpnUiPlugin::importConnectionSettings(const QString&)':
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:490:112: error: no matching function for call to 'OpenVpnUiPlugin::saveFile(QTextStream&, QLatin1String, const QString&, const char [7])'
             const QString caAbsolutePath = saveFile(in, QLatin1String(END_KEY_CA_TAG), connectionName, "ca.crt");
                                                                                                                ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:490:112: note: candidate is:
In file included from /var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:24:0:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note: QString OpenVpnUiPlugin::saveFile(int&, const QString&, const QString&, const QString&)
     QString saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName);
             ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note:   no known conversion for argument 1 from 'QTextStream' to 'int&'
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:496:118: error: no matching function for call to 'OpenVpnUiPlugin::saveFile(QTextStream&, QLatin1String, const QString&, const char [9])'
             const QString certAbsolutePath = saveFile(in, QLatin1String(END_KEY_CERT_TAG), connectionName, "cert.crt");
                                                                                                                      ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:496:118: note: candidate is:
In file included from /var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:24:0:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note: QString OpenVpnUiPlugin::saveFile(int&, const QString&, const QString&, const QString&)
     QString saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName);
             ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note:   no known conversion for argument 1 from 'QTextStream' to 'int&'
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:502:119: error: no matching function for call to 'OpenVpnUiPlugin::saveFile(QTextStream&, QLatin1String, const QString&, const char [12])'
             const QString keyAbsolutePath = saveFile(in, QLatin1String(END_KEY_KEY_TAG), connectionName, "private.key");
                                                                                                                       ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:502:119: note: candidate is:
In file included from /var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:24:0:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note: QString OpenVpnUiPlugin::saveFile(int&, const QString&, const QString&, const QString&)
     QString saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName);
             ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note:   no known conversion for argument 1 from 'QTextStream' to 'int&'
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:508:124: error: no matching function for call to 'OpenVpnUiPlugin::saveFile(QTextStream&, QLatin1String, const QString&, const char [11])'
             const QString secretAbsolutePath = saveFile(in, QLatin1String(END_KEY_SECRET_TAG), connectionName, "secret.key");
                                                                                                                            ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:508:124: note: candidate is:
In file included from /var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:24:0:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note: QString OpenVpnUiPlugin::saveFile(int&, const QString&, const QString&, const QString&)
     QString saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName);
             ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note:   no known conversion for argument 1 from 'QTextStream' to 'int&'
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:519:125: error: no matching function for call to 'OpenVpnUiPlugin::saveFile(QTextStream&, QLatin1String, const QString&, const char [13])'
             const QString tlsAuthAbsolutePath = saveFile(in, QLatin1String(END_TLS_AUTH_TAG), connectionName, "tls_auth.key");
                                                                                                                             ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:519:125: note: candidate is:
In file included from /var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:24:0:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note: QString OpenVpnUiPlugin::saveFile(int&, const QString&, const QString&, const QString&)
     QString saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName);
             ^
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: note:   no known conversion for argument 1 from 'QTextStream' to 'int&'
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp: At global scope:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:607:9: error: prototype for 'QString OpenVpnUiPlugin::saveFile(QTextStream&, const QString&, const QString&, const QString&)' does not match any in class 'OpenVpnUiPlugin'
 QString OpenVpnUiPlugin::saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName)
         ^
In file included from /var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.cpp:24:0:
/var/tmp/paludis/build/kde-plasma-nm-0.9.3.4/work/plasma-nm-0.9.3.4/vpn/openvpn/openvpn.h:46:13: error: candidate is: QString OpenVpnUiPlugin::saveFile(int&, const QString&, const QString&, const QString&)
     QString saveFile(QTextStream &in, const QString &endTag, const QString &connectionName, const QString &fileName);
             ^
vpn/openvpn/CMakeFiles/plasmanetworkmanagement_openvpnui.dir/build.make:95: recipe for target 'vpn/openvpn/CMakeFiles/plasmanetworkmanagement_openvpnui.dir/openvpn.cpp.o' failed


Installed Qt4 version is 4.8.6 and the previous release of plasma-nm (0.9.3.3) builds fine.