Report codegen timings for binary crates

[epage]

Problem

Currently --timings doesn't report codegen timings for binary crates.

Proposed Solution

• Emit unused metadata for bin's so codegen timings get reported
• Or waiting for Add --json=timings option to print build timings compiler-team#873

Notes

Created from

• Report codegen timings for binary crates #10960
• https://rust-lang.zulipchat.com/#narrow/stream/246057-t-cargo/topic/reporting.20codegen.20timings.20for.20binary.20crates