slibtool: update to 0.5.19

Changes:
This patch release includes several improvements in the driver logic,
as well as one important fix to the compile mode logic.

- driver: support -export-dynamic.
- driver: allow flavor-based use of native tools (ar,ranlib,etc.)
- driver: slbt_init_host_params(): improve native target detection logic.
- driver: -shrext support: only use the extension portion of the extension.
- compile mode: gnu libtool compatibility: do not add -c to compiler arguments.

(wiedi)