www/qt5-webengine does not build on 14.0-x and 15.0-CURRENT

[Rainer Hurling]

Dear KDE-Team, dear devs,

On 14.0-x and 15.0-CURRENT, I am no longer able to build 
www/qt5-webengine. The following error is triggered in an unclean 
environment and even in Poudriere:


[ 49% 12002/24388] CXX 
obj/gpu/command_buffer/service/gles2_sources/program_manager.o
FAILED: obj/gpu/command_buffer/service/gles2_sources/program_manager.o
[..snip..]
../../../../qtwebengine-everywhere-src-5.15.8/src/3rdparty/chromium/gpu/command_buffer/service/program_manager.cc:627:25: 
error: no member named 'as_string' in 'absl::string_view'
   return output + input.as_string();
                   ~~~~~ ^

If a full build log is needed, I can provide it. Thanks in advance for 
any help.

Best wishes,
Rainer Hurling