Try --disable-split-debug for distro-configs/Jenkins/linux_clang_dbgutil_64

...in the hope that it will fix gdb backtrace generation for those Jenkins builds,
as just discussed on Freenode #libreoffice-dev:

> Apr 09 14:03:47 <sberg> mst___, cloph, didn't you discuss broken gdb
>  backtraces on some Jenkins bots the other day?
>  <https://ci.libreoffice.org/job/gerrit_linux_clang_dbgutil/56703/console> is
>  another example of the bt for thread 1 missing, probably because gdb went
>  south or something
> Apr 09 14:06:05 <llunak> sberg: that looks like gdb is too old to handle debug
>  info produced by that clang version
> Apr 09 14:08:05 <llunak> sberg: and presumably --disable-split-debug would be
>  a workaround with some (not sure how big) performance cost
> Apr 09 14:11:43 <mst___> yeah there were lots of complaints about
>  incomprehensible DWARFs in that log

Change-Id: I69aa80fdd13148330d00231eefe37cbf965fe4d6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/91970
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

distro-configs/Jenkins/linux_clang_dbgutil_64

@@ -4,3 +4,4 @@ COMPILER_PLUGINS_CXX=ccache g++ -std=c++11
 --enable-kf5
 --disable-compiler-plugins-analyzer-pch
 --disable-dependency-tracking
+--disable-split-debug