symlinking is not working as expected on `x build`

[onur-ozkan]

Because of the early return here:

rust/src/bootstrap/compile.rs

Lines 1331 to 1335 in 3d7a091

	return INTERNER.intern_path(sysroot);
	}
	// Symlink the source root into the same location inside the sysroot,
	// where `rust-src` component would go (`$sysroot/lib/rustlib/src/rust`),

symlinking phases are bypassed which causes tools like miri can't find rust-src.