SUMMARY
***
In Centos7, I want to compile the KXMLGUI. The version of my Qt is 5.15.10. The version of KXMLGUI is v5.106.0. During the compilation, I encountered a compilation error：home/xxx/KDEFrameworks/kxmlgui-v5.106.0/src/ksendbugmail/smtp.cpp:158:16: error: expected type-specifier before 'QSslSocket' 
sock = new QSslSocket(this);
***


STEPS TO REPRODUCE
1. download the kxmlgui from https://invent.kde.org/frameworks/kxmlgui/-/tree/v5.106.0?ref_type=tags and decompress the package
2. go to the package and mkdir build
3. cd build
4 cmake .. , wait a moment and it shows the infomation:  
    -- Configuring done
    -- Generating done
     -- Build files have been written to xxx/build
5 make
   then  I encountered a compilation error
OBSERVED RESULT
 During the compilation, I encountered a compilation error：home/xxx/KDEFrameworks/kxmlgui-v5.106.0/src/ksendbugmail/smtp.cpp:158:16: error: expected type-specifier before 'QSslSocket' 
sock = new QSslSocket(this);
EXPECTED RESULT
Compiled successfully.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: Centos7
(available in About System)
KDE Plasma Version: 1.10
KDE Frameworks Version: 
Qt Version: 5.15.10

ADDITIONAL INFORMATION
I tried Qt version 5.15.0 and kxmlgui version v100.0 and the error was the same.