Eli Schwartz authored Jun 25, 2019 and Allan McRae committed Jun 28, 2019

The default state of `dependency()` is `required: true`, which means if
a dependency is not found, meson immediately aborts and does not log our
`error()` messages. meson 0.50 has builtin support for dependencies with
custom error messages.

The alternative would be to specify `required: false` everywhere, and
only then to key off of `dep.found()`.

Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>
Signed-off-by: Allan McRae <allan@archlinux.org>