Remove jobserver Client from Session

We want to restrict access to the raw Client and this is the first step
to doing so; the client is still initialized from the environment at the
same time.

Author: Mark-Simulacrum

src/librustc_codegen_ssa/back/write.rs

@@ -433,7 +433,7 @@ pub fn start_async_codegen<B: ExtraBackendMethods>(
                                                   codegen_worker_send,
                                                   coordinator_receive,
                                                   total_cgus,
-                                                  sess.jobserver.clone(),
+                                                  rustc_jobserver::client(),
                                                   Arc::new(modules_config),
                                                   Arc::new(metadata_config),
                                                   Arc::new(allocator_config),

src/librustc_jobserver/lib.rs

@@ -29,6 +29,10 @@ lazy_static! {
     };
 }
 
+pub fn initialize() {
+    lazy_static::initialize(&GLOBAL_CLIENT)
+}
+
 pub fn client() -> Client {
     GLOBAL_CLIENT.clone()
 }

src/librustc_session/session.rs

@@ -31,7 +31,6 @@ use syntax_pos::{MultiSpan, Span};
 
 use rustc_target::spec::{PanicStrategy, RelroLevel, Target, TargetTriple};
 use rustc_data_structures::flock;
-use rustc_jobserver::{self as jobserver, Client};
 use rustc_data_structures::profiling::{SelfProfiler, SelfProfilerRef};
 
 use std;
@@ -121,10 +120,6 @@ pub struct Session {
     /// Always set to zero and incremented so that we can print fuel expended by a crate.
     pub print_fuel: AtomicUsize,
 
-    /// Loaded up early on in the initialization of this `Session` to avoid
-    /// false positives about a job server in our environment.
-    pub jobserver: Client,
-
     /// Cap lint level specified by a driver specifically.
     pub driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
 
@@ -1131,6 +1126,8 @@ fn build_session_(
         CguReuseTracker::new_disabled()
     };
 
+    rustc_jobserver::initialize();
+
     let sess = Session {
         target: target_cfg,
         host,
@@ -1163,7 +1160,6 @@ fn build_session_(
         optimization_fuel,
         print_fuel_crate,
         print_fuel,
-        jobserver: jobserver::client(),
         driver_lint_caps,
         trait_methods_not_found: Lock::new(Default::default()),
         confused_type_with_std_module: Lock::new(Default::default()),