Documentation: Add option to treat Doxygen warnings as errors

A new Doxygen warning introduced in a recent commit went unnoticed, both
in manual tests and in CI. Unlike C/C++ warnings that are treated as
errors, we don't fail the build with Doxygen warnings. This is due to
the fact that the libcamera documentation compiles cleanly only with quite
recent versions of Doxygen. Enabling the WARN_AS_ERROR Doxygen option
unconditionally could bother many users.

To improve the situation, add a meson option to treat Doxygen warnings
as errors. The option is disabled by default, preserving the current
behaviour, and will be enabled in CI builds.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

Documentation/Doxyfile.in

@@ -20,6 +20,7 @@ TOC_INCLUDE_HEADINGS   = 0
 CASE_SENSE_NAMES       = YES
 
 QUIET                  = YES
+WARN_AS_ERROR          = @WARN_AS_ERROR@
 
 INPUT                  = "@TOP_SRCDIR@/include/libcamera" \
                          "@TOP_SRCDIR@/src/ipa/ipu3" \

Documentation/meson.build

@@ -15,6 +15,7 @@ if doxygen.found() and dot.found()
     cdata.set('TOP_SRCDIR', meson.project_source_root())
     cdata.set('TOP_BUILDDIR', meson.project_build_root())
     cdata.set('OUTPUT_DIR', meson.current_build_dir())
+    cdata.set('WARN_AS_ERROR', get_option('doc_werror') ? 'YES' : 'NO')
 
     doxygen_predefined = []
     foreach key : config_h.keys()