We were looking for the cups headers and the cups lib in the default locations
which for example breaks with OpenBSD where the cups headers are under /usr/local/include/
Instead just use the "cups" dependency type from meson which internally uses cups-config.
Fixes#1967
In 9236ee0564 the cups code was updated to use newer API with cups >= 2
and a later commit (a7e207abe) dropped the old code paths and added version
checks in meson/autotools.
The newly used functions were httpConnect2 and httpReconnect2 which are
available since 1.7 and don't require cups 2.0.
Change the versions checks to 1.7 instead so gtk can still be build with
older cups (macOS 10.9 for example, see #1950)
httpGetAuthString() was added with cups 1.3 and we depend on a newer version
now. The direct field access was a fallback in case httpGetAuthString()
was missing, so this can also be dropped.
Various adjustments to make the config.h output between autotools
and meson more similar by testing on Linux and Windows/MSYS2.
Setting things to 1 instead of true and shifting things around is motivated
by reducing the diff between the generated files.
This changes the configure option into two states:
auto: build all that can be build (default)
A list of backend names: build them and fail if we can't
"papi" is missing because it's not in Debian and I can't test it.
