bug#34062: qtwebkit-5.212.0-alpha2 parallel build failure

[Ludovic Courtès]

Or sometimes like this:

--8<---------------cut here---------------start------------->8---
[ 81%] Generating 
../../DerivedSources/WebKit2/AuthenticationManagerMessageReceiver.cpp, 
../../DerivedSources/WebKit2/AuthenticationManagerMessages.h
cd 
/tmp/guix-build-qtwebkit-5.212.0-alpha2.drv-0/qtwebkit-5.212.0-alpha2/Source/WebKit2
 && /gnu/store/g87hamjyipk1j6dfq5pjfzfnfb64spbv-python2-2.7.15/bin/python2.7 
/tmp/guix-build-qtwebkit-5.212.0-alpha2.drv-0/qtwebkit-5.212.0-alpha2/Source/WebKit2/Scripts/generate-message-receiver.py
 Shared/Authentication/AuthenticationManager.messages.in > 
/tmp/guix-build-qtwebkit-5.212.0-alpha2.drv-0/build/DerivedSources/WebKit2/AuthenticationManagerMessageReceiver.cpp
Traceback (most recent call last):
  File 
"/tmp/guix-build-qtwebkit-5.212.0-alpha2.drv-0/qtwebkit-5.212.0-alpha2/Source/WebKit2/Scripts/generate-message-receiver.py",
 line 28, in <module>
    import webkit.messages
EOFError: EOF read where object expected
cd 
/tmp/guix-build-qtwebkit-5.212.0-alpha2.drv-0/qtwebkit-5.212.0-alpha2/Source/WebKit2
 && /gnu/store/g87hamjyipk1j6dfq5pjfzfnfb64spbv-python2-2.7.15/bin/python2.7 
/tmp/guix-build-qtwebkit-5.212.0-alpha2.drv-0/qtwebkit-5.212.0-alpha2/Source/WebKit2/Scripts/generate-messages-header.py
 NetworkProcess/NetworkResourceLoader.messages.in > 
/tmp/guix-build-qtwebkit-5.212.0-alpha2.drv-0/build/DerivedSources/WebKit2/NetworkResourceLoaderMessages.h
make[2]: *** [Source/WebKit2/CMakeFiles/WebKit2.dir/build.make:194: 
DerivedSources/WebKit2/ChildProcessMessageReceiver.cpp] Error 1
--8<---------------cut here---------------end--------------->8---

See
<https://ci.guix.info/log/901miwpk9srhwq3646v6bm7zni3qda8m-qtwebkit-5.212.0-alpha2>.

Interestingly this was first reported here for WebkitGTK:
<https://issues.guix.info/issue/30015>.

Did the issue vanish for WebkitGTK?  Qtwebkit is older so it may well
miss an upstream fix.

Thanks,
Ludo’.