LabPlot builds and runs with kf5

[Alexander Semke]

> Is xlocale.h not included for some reason on OSX? How can I check whether it
> is?
xlocale.h is included in locale.h if __USE_XOPEN2K8 is defined. This should be 
the case when the GNU part of the glibc is used. Can you try to compile 
everything with the flag -D_GNU_SOURCE? Just add this flag to the cmake's 
DCMAKE_CXX_FLAGS like in our compile script.

-- 
Alexander