adds crds-value for broadcasting duplicate shreds through gossip (#14133)

In gossip, the header overhead we get from:
https://github.com/solana-labs/solana/blob/de9ac43eb/core/src/cluster_info.rs#L434-L435
https://github.com/solana-labs/solana/blob/de9ac43eb/core/src/crds_value.rs#L31-L36
https://github.com/solana-labs/solana/blob/de9ac43eb/core/src/crds_value.rs#L73
already exceeds SIZE_OF_NONCE in shreds. We also need aditional
meta-data (wallclock, source pubkey, ...). Which means that given the
SHRED_PAYLOAD_SIZE, we cannot fit all these in PACKET_DATA_SIZE:
https://github.com/solana-labs/solana/blob/de9ac43eb/ledger/src/shred.rs#L80

On top of that, we need 2 shred payloads as the proof of duplicate. So
each DuplicateShred crds value includes only a chunk of the payload,
along with the meta-data to reconstruct the full payload from the chunks
on the receiving end.

ledger/build.rs

@@ -0,0 +1,27 @@
+extern crate rustc_version;
+use rustc_version::{version_meta, Channel};
+
+fn main() {
+    // Copied and adapted from
+    // https://github.com/Kimundi/rustc-version-rs/blob/1d692a965f4e48a8cb72e82cda953107c0d22f47/README.md#example
+    // Licensed under Apache-2.0 + MIT
+    match version_meta().unwrap().channel {
+        Channel::Stable => {
+            println!("cargo:rustc-cfg=RUSTC_WITHOUT_SPECIALIZATION");
+        }
+        Channel::Beta => {
+            println!("cargo:rustc-cfg=RUSTC_WITHOUT_SPECIALIZATION");
+        }
+        Channel::Nightly => {
+            println!("cargo:rustc-cfg=RUSTC_WITH_SPECIALIZATION");
+        }
+        Channel::Dev => {
+            println!("cargo:rustc-cfg=RUSTC_WITH_SPECIALIZATION");
+            // See https://github.com/solana-labs/solana/issues/11055
+            // We may be running the custom `rust-bpf-builder` toolchain,
+            // which currently needs `#![feature(proc_macro_hygiene)]` to
+            // be applied.
+            println!("cargo:rustc-cfg=RUSTC_NEEDS_PROC_MACRO_HYGIENE");
+        }
+    }
+}