All packages that use Meson are built with -O0

[Jonathan Schleifer <js%NetBSD.org@localhost>]

As I just noticed, we build all packages that use Meson with -O0, as I 
was hinted at by building something using Meson on Linux:

414 | #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)

The reason is that we use buildtype=plain, which means debug=false and 
optimization=plain -- which is -O0.

I committed a fix, as it seemed like an obvious bug, but then realized 
that we've been running on -O0 for years, so there's a chance of 
breaking things, so I quickly reverted it.

How do we want to move forward? I think we really should not build 
everything that uses Meson with -O0. Changing that to -O2 instead will 
probably make all desktops on NetBSD a *lot* faster.

Related: Do we want to add -Db_pie=true at the same time?

--
Jonathan