Change cfg parsers to produce symbols instead of strings.

compiler/rustc_interface/src/tests.rs

@@ -26,8 +26,8 @@ use rustc_session::{build_session, getopts, Session};
 use rustc_session::{CompilerIO, EarlyErrorHandler};
 use rustc_span::edition::{Edition, DEFAULT_EDITION};
 use rustc_span::symbol::sym;
-use rustc_span::FileName;
 use rustc_span::SourceFileHashAlgorithm;
+use rustc_span::{FileName, Symbol};
 use rustc_target::spec::{CodeModel, LinkerFlavorCli, MergeFunctions, PanicStrategy, RelocModel};
 use rustc_target::spec::{RelroLevel, SanitizerSet, SplitDebuginfo, StackProtector, TlsModel};
 use std::collections::{BTreeMap, BTreeSet};
@@ -38,7 +38,7 @@ use std::sync::Arc;
 fn mk_session(
     handler: &mut EarlyErrorHandler,
     matches: getopts::Matches,
-) -> (Session, Cfg<String>) {
+) -> (Session, Cfg<Symbol>) {
     let registry = registry::Registry::new(&[]);
     let sessopts = build_session_options(handler, &matches);
     let cfg = parse_cfg(handler, matches.opt_strs("cfg"));