Make rustc implicitly use panic=abort for the panic_abort crate

The panic_abort crate must be compiled with panic=abort, but cargo
doesn't allow setting the panic strategy for a single crate. Bootstrap
handles this in its rustc wrapper, but for example the build systems of
cg_clif and cg_gcc don't use a rustc wrapper, so they would either need
to add one or be unable to build a sysroot suitable for both panic=abort
and panic=unwind (as is currently the case).

Author: bjorn3

compiler/rustc_session/src/session.rs

@@ -693,6 +693,11 @@ impl Session {
     /// Returns the panic strategy for this compile session. If the user explicitly selected one
     /// using '-C panic', use that, otherwise use the panic strategy defined by the target.
     pub fn panic_strategy(&self) -> PanicStrategy {
+        if self.opts.crate_name.as_deref() == Some("panic_abort") {
+            // The panic_abort crate must always be compiled with panic=abort.
+            return PanicStrategy::Abort;
+        }
+
         self.opts.cg.panic.unwrap_or(self.target.panic_strategy)
     }
 

src/bootstrap/src/bin/rustc.rs

@@ -151,18 +151,6 @@ fn main() {
             cmd.arg("--sysroot").arg(&sysroot);
         }
 
-        // If we're compiling specifically the `panic_abort` crate then we pass
-        // the `-C panic=abort` option. Note that we do not do this for any
-        // other crate intentionally as this is the only crate for now that we
-        // ship with panic=abort.
-        //
-        // This... is a bit of a hack how we detect this. Ideally this
-        // information should be encoded in the crate I guess? Would likely
-        // require an RFC amendment to RFC 1513, however.
-        if crate_name == Some("panic_abort") {
-            cmd.arg("-C").arg("panic=abort");
-        }
-
         let crate_type = parse_value_from_args(&orig_args, "--crate-type");
         // `-Ztls-model=initial-exec` must not be applied to proc-macros, see
         // issue https://github.com/rust-lang/rust/issues/100530