Implement --check-cfg option (RFC 3013)

Co-authored-by: Urgau <lolo.branstett@numericable.fr>
Co-authored-by: Marcelina Kościelnicka <mwk@0x04.net>

src/librustdoc/core.rs

@@ -250,6 +250,7 @@ crate fn create_config(
     interface::Config {
         opts: sessopts,
         crate_cfg: interface::parse_cfgspecs(cfgs),
+        crate_check_cfg: interface::parse_check_cfg(vec![]),
         input,
         input_path: cpath,
         output_file: None,

src/librustdoc/doctest.rs

@@ -91,6 +91,7 @@ crate fn run(options: RustdocOptions) -> Result<(), ErrorReported> {
     let config = interface::Config {
         opts: sessopts,
         crate_cfg: interface::parse_cfgspecs(cfgs),
+        crate_check_cfg: interface::parse_check_cfg(vec![]),
         input,
         input_path: None,
         output_file: None,