Stop trying to maintain a per-file _POSIX_C_SOURCE. Instead,
require POSIX.1-2008 globally. A lot of core source files depend
on that already.
Some care must be taken on a few select files where we need a bit
more than POSIX. Some files need XSI extensions (_XOPEN_SOURCE) and
some files need BSD extensions (_DEFAULT_SOURCE). In both cases,
these feature test macros imply _POSIX_C_SOURCE. Make sure to not
define both these macros and _POSIX_C_SOURCE explicitly to avoid
POSIX requirement conflicts (e.g. _POSIX_C_SOURCE says POSIX.1-2001
but _XOPEN_SOURCE says POSIX.1-2008).
Additionally, there is one special case in render/vulkan/vulkan.c.
That file needs major()/minor(), and these are system-specific.
On FreeBSD, _POSIX_C_SOURCE hides system-specific symbols so we need
to make sure it's not defined for this file. On Linux, we can
explicitly include <sys/sysmacros.h> and ensure that apart from
symbols defined there the file only uses POSIX toys.
We can just assume CLOCK_MONOTONIC everywhere.
Simplifies the backend API, and fixes clock mismatches when multiple
backends are used together with different clocks.
The backend is not able to tell whether a surface is being
presented via direct scan-out or not. The backend will set
ZERO_COPY if the buffer submitted via the output commit was
presented in a zero-copy fashion, but will no know whether the
buffer comes from the compositor or the client.
Some globals are static and it doesn't make sense to destroy them before
the wl_display. For instance, wl_compositor should be created before the
display is started and shouldn't be destroyed.
For these globals, we can simplify the code by removing the destructor
and stop keeping track of wl_resources (these will be destroyed with the
wl_display by libwayland).
Most of the time, compositors just display the surface's current buffer
on an output. Add an helper to make it easy to support presentation-time
in this case.
The wlr_presentation_feedback struct now tracks presentation feedback
for multiple resources (but still a single surface content update). This
allows the compositor to properly send presentation events even when
there is more than one frame of latency or when it references a
surface's buffer.