Pass -Cpanic=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 the usual
way using panic="abort", but luckily per-package rustflags do allow
this. Bootstrap previously handled this in its rustc wrapper, but for
example the build systems of cg_clif and cg_gcc don't use the rustc
wrapper, so they would either need to add one, patch the standard
library or be unable to build a sysroot suitable for both panic=abort
and panic=unwind (as is currently the case).

Author: bjorn3

library/Cargo.toml

@@ -1,3 +1,5 @@
+cargo-features = ["profile-rustflags"]
+
 [workspace]
 resolver = "1"
 members = [
@@ -44,6 +46,14 @@ object.debug = 0
 rustc-demangle.debug = 0
 rustc-demangle.opt-level = "s"
 
+# panic_abort must always be compiled with panic=abort, even when the rest of the
+# sysroot is panic=unwind.
+[profile.dev.package.panic_abort]
+rustflags = ["-Cpanic=abort"]
+
+[profile.release.package.panic_abort]
+rustflags = ["-Cpanic=abort"]
+
 [patch.crates-io]
 # See comments in `library/rustc-std-workspace-core/README.md` for what's going on
 # here

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