Log Message:
slibtool: update to 0.5.18

Changelog:
  This patch release includes several important fixes to the link mode
  and driver logic. In addition, it adds mdso support to midipix targets,
  as well as updates slibtool's own build system.

  - link mode: re-implemented slbt_exec_link_finalize_argument_vector().
  - link mode: import library generation: added mdso support.
  - link mode: use -fpic objects with -disable-static.
  - driver: added --mdso and --implib support.
  - driver: added initial -dlpreopen support.
  - driver: support -thread-safe more elegantly.
  - driver: properly handle -thread-safe (no-op, compatibility).