Fixes nullptr dereference (regression by commit df5f9f4a).

Prepare for providing everything in a shared library, to be embedded
in another process.

Ignore the storage configuration if FLAG_REQUIRE_STORAGE is not set in
the DatabasePlugin.

The new method IsPlugin() replaces the "is_simple" flag.

Use a listener interface instead of GlobalEvents.

Build was broken by previous commit.

Fix build failure.

Fixes hanging child process in the "pipe" output plugin.

Link libvorbisfile first, followed to libvorbis and finally libogg.
This order is necessary because libvorbisfile depends on libvorbis.

Bionic doesn't have the SYS_* macros.

Use it if it exists, but don't insist if the C library is poor
(e.g. Bionic/Android).

Bionic's pthread declarations are non-literal.

Required for building without GLib.