Log Message:
kate: fix builds for some platforms (e.g., NetBSD 9.x)

In some contexts, use of PCH causes build failures, e.g.:

[  9%] Building C object pch/CMakeFiles/katepch.dir/cmake_pch.h.gch
[  9%] Building CXX object \ 
pch/CMakeFiles/katepch.dir/katepch_autogen/mocs_compilation.cpp.o
[  9%] Building CXX object \ 
addons/backtracebrowser/autotests/CMakeFiles/btbrowser_test.dir/__/btparser.cpp. \ 
o
<command-line>: fatal error: had to relocate PCH
compilation terminated.
--- pch/CMakeFiles/katepch.dir/katepch_autogen/mocs_compilation.cpp.o ---
*** [pch/CMakeFiles/katepch.dir/katepch_autogen/mocs_compilation.cpp.o] Error code 1

The upstream project offers the configuration option to disable PCH, so
take advantage of this. Except, evidently they have not recently tested
a build with that setting disabled, as various files then miss specific
includes that happen to get covered with their catch-all pch.h header.

While here, also don't install .desktop files as executable, they are
not scripts (and this one wouldn't magically work anyway).