Support building solana-program on 32-bit architectures that do not (#21577)

have 64-bit atomics by using a Mutex<u64> on 32-bit architectures.

Currently the usage of atomics are only in functions that support
tests and benchmarks.

sdk/program/src/lib.rs

@@ -6,6 +6,7 @@
 extern crate self as solana_program;
 
 pub mod account_info;
+pub(crate) mod atomic_u64;
 pub mod blake3;
 pub mod borsh;
 pub mod bpf_loader;