build: disable -Wdocumentation-deprecated-sync

We will never remove the deprecated functions and there is no real
reason to annoy users into stop using them.

If there *will* be a reason, *then* we will add the attribute.

Fixes: https://github.com/xkbcommon/libxkbcommon/issues/56
Signed-off-by: Ran Benita <ran234@gmail.com>

configure.ac

@@ -85,7 +85,7 @@ AM_CONDITIONAL(BUILD_LINUX_TESTS, [test "x$ac_cv_header_linux_input_h" = xyes])
 
 XORG_TESTSET_CFLAG([BASE_CFLAGS], [-fvisibility=hidden])
 XORG_TESTSET_CFLAG([BASE_CFLAGS], [-Wextra -Wno-unused-parameter -Wno-missing-field-initializers])
-XORG_TESTSET_CFLAG([BASE_CFLAGS], [-Wdocumentation])
+XORG_TESTSET_CFLAG([BASE_CFLAGS], [-Wdocumentation -Wno-documentation-deprecated-sync])
 
 # OpenBSD does not have DT_NEEDED entries for libc by design
 # so when these flags are passed to ld via libtool the checks will fail

meson.build

@@ -30,6 +30,7 @@ foreach cflag: [
     '-Wlogical-op',
     '-Wdate-time',
     '-Wwrite-strings',
+    '-Wno-documentation-deprecated-sync',
 ]
     if cc.has_argument(cflag)
         add_project_arguments(cflag, language: 'c')