$ meson setup build -Dwebp=disabled
$ meson compile -C build

[..]
../libvips/foreign/webpsave.c:1254:21: error: unknown type name 'VipsImage'
vips_webpsave_mime( VipsImage *in, ... )
                    ^
../libvips/foreign/webpsave.c:1260:11: error: implicit declaration of function 'vips_call_split' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        result = vips_call_split( "webpsave_mime", ap, in );
                 ^
../libvips/foreign/webpsave.c:1295:23: error: unknown type name 'VipsImage'
vips_webpsave_target( VipsImage *in, VipsTarget *target, ... )
                      ^
../libvips/foreign/webpsave.c:1295:38: error: unknown type name 'VipsTarget'
vips_webpsave_target( VipsImage *in, VipsTarget *target, ... )
                                     ^
../libvips/foreign/webpsave.c:1301:11: error: implicit declaration of function 'vips_call_split' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        result = vips_call_split( "webpsave_target", ap, in, target );
                 ^
1 warning and 19 errors generated.
[69/505] Compiling C object libvips/deprecated/libdeprecated.a.p/freq_dispatch.c.o
ninja: build stopped: subcommand failed.

$ meson setup build -Dwebp=disabled
$ meson compile -C build

[..]
[505/505] Linking target cplusplus/libvips-cpp.42.dylib