disable split debug if --enable-lto
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88389 is right that
split-debug doesn't make sense with LTO. Without -ffat-lto-objects
or with Clang .o files aren't even really object files that
would be normally usable. Since gcc complains if the combination
is used, explicitly avoid it.
Change-Id: I76992e94f4790238e5aaee691b5cec54fd0ef3a0
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/125379
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>