Meson: Do not always generate static library

Since Meson 0.46.0 'default_library' can be set to 'both' when user
wants both shared and static libraries.
2 jobs for <span class="ref-name">meson-library</span> in 45 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #247299
debian sid

00:00:45

failed #247298
debian sid

00:01:35