meson: Correctly pass the global include to the compiler

It's not safe to assume `-include config.h` works, since this depends on
the functionality of the compiler that the cwd when running the compiler
is searched first.

When libcamera is included as a Meson subproject, the cwd of the
compiler is the cwd of the main project, not of libcamera's build dir,
and thus cannot be found. Instead, pass the include filename as a path
based on the current build dir.

Signed-off-by: Eli Schwartz <eschwartz93@gmail.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

meson.build

@@ -44,7 +44,7 @@ endif
 
 common_arguments = [
     '-Wshadow',
-    '-include', 'config.h',
+    '-include', meson.current_build_dir() / 'config.h',
 ]
 
 c_arguments = []