xkeyboard-config: Turn absolute symlinks into relative

xkeyboard-config: Turn absolute symlinks into relative

Native builds encode symlinks pointing to absolute paths into
build native sysroot which gets into sstate artifacts and an error
is rightly generated

ERROR: xkeyboard-config-native-2.45-r0 do_populate_sysroot: sstate found an absolute path symlink /mnt/b/yoe/master/build/tmp/work/x86_64-linux/xkeyboard-config-native/2.45/sysroot-destdir/mnt/b/yoe/master/build/tmp/work/x86_64-linux/xkeyboard-config-native/2.45/recipe-sysroot-native/usr/share/X11/xkb pointing at /mnt/b/yoe/master/build/tmp/work/x86_64-linux/xkeyboard-config-native/2.45/recipe-sysroot-native/usr/share/xkeyboard-config-2. Please replace this with a relative link.
ERROR: xkeyboard-config-native-2.45-r0 do_populate_sysroot: Failing task due to absolute path symlinks

Turn these symlinks to be relative inside D which will reflect
correclty without need for absolute path prefix

Suggested-by: Zoltán Böszörményi <zboszor@gmail.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>