Fix bootstrap failure when multilibs are enabled.

Upstream-Status: Backport [https://github.com/rust-lang/rust/commit/139d6ba054a1a4cc5fe64981ad46fd5547bd4916]

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
---
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index 066e6bf53f..a2f6fac4b1 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -646,7 +646,10 @@ impl Builder<'_> {
                 // Build proc macros both for the host and the target unless proc-macros are not
                 // supported by the target.
                 if target != compiler.host && cmd_kind != Kind::Check {
-                    let error = command(self.rustc(compiler))
+                    let mut rustc_cmd = command(self.rustc(compiler));
+                    self.add_rustc_lib_path(compiler, &mut rustc_cmd);
+
+                    let error = rustc_cmd
                         .arg("--target")
                         .arg(target.rustc_target_arg())
                         .arg("--print=file-names")
@@ -654,6 +657,7 @@ impl Builder<'_> {
                         .arg("-")
                         .run_capture(self)
                         .stderr();
+
                     let not_supported = error
                         .lines()
                         .any(|line| line.contains("unsupported crate type `proc-macro`"));