D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082
Usage:
pkgconfig.generate(
...
description : 'A library with custom variables.',
variables : ['foo=bar', 'datadir=${prefix}/data']
)
The variables 'prefix', 'libdir' and 'includedir' are reserved, meson will
fail with an error message.
Variables can reference each other with the pkgconfig notation, e.g.
variables : ['datadir=${prefix}/data',
'otherdatadir=${datadir}/other']
meson does not check this for correctness or that the referenced variable
exists, we merely keep the same order as specified.