meson: Convert attr_dep to dependency()

Currently, libattr is detected using cc.find_library() because at
historically, the library was lacking pkg-config file. But that
changed with libattr-2.4.48 (released 7+ years ago) and even
prehistoric distros have it now. Switch to dependency().

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

meson.build

@@ -919,8 +919,7 @@ if not get_option('apparmor_profiles').disabled()
   endif
 endif
 
-# FIXME rewrite to use dependency() once we can use 2.4.48
-attr_dep = cc.find_library('attr', required: get_option('attr'))
+attr_dep = dependency('libattr', required: get_option('attr'))
 if attr_dep.found()
   conf.set('WITH_LIBATTR', 1)
 endif