Add support for deprecated loader (#11946)

sdk/src/bpf_loader.rs

@@ -1 +1,17 @@
+//! @brief The latest Solana BPF loader.
+//!
+//! The BPF loader is responsible for loading, finalizing, and executing BPF
+//! programs.  Not all networks may support the latest loader.  You can use the
+//! command-line tools to check if this version of the loader is supported by
+//! requesting the account info for the public key below.
+//!
+//! The program format may change between loaders, and it is crucial to build
+//! your program against the proper entrypoint semantics.  All programs being
+//! deployed to this BPF loader must build against the latest entrypoint version
+//! located in `entrypoint.rs`.
+//!
+//! Note: Programs built for older loaders must use a matching entrypoint
+//! version.  An example is `bpf_loader_deprecated.rs` which requires
+//! `entrypoint_deprecated.rs`.
+
 crate::declare_id!("BPFLoader2111111111111111111111111111111111");