Restore compat. with mainnet-beta

[ryoqun]

Problem

After long bisecting, I've finally tracked down what causing master to be incompatibile with mainnet-beta (v1.2).

Summary of Changes

After spotting this, I couldn't fix this easily. So, I'm just sharing what I found...

Obviously, this is rather work-around, needs proper fix.. But, this restores compatibility at least...

Fixes #

[ryoqun]

@jackcmay It seems that some of mainnet-beta's programs executes Ok on v1.2, but fails with UnalignedPointer on master.

[ryoqun]

 bank] result: 673XSffuWqYJ6TQeSYZrWXjRZmQqqGxbreUP75jo7TtJ1tk58JiHRCuNCsrEMr8vH1qB19UxQdkgzzetVSUrJRfp => Ok(())
-bank] result: 8vNyVCumvrNzdHrbRNgQkpDG1syXELCxqF9SCd5ukexhr4RgENxbZAJkbeFvWdPoEK9RzFDLJrVyf8QPN2pkroj => Ok(())
+bank] result: 8vNyVCumvrNzdHrbRNgQkpDG1syXELCxqF9SCd5ukexhr4RgENxbZAJkbeFvWdPoEK9RzFDLJrVyf8QPN2pkroj => Err(InstructionError(1, Custom(194969602)))
 bank] result: 97Teou5Ef3TZ2PiPm11ftvFqfgWpynhuMEGcCxmmHbf7wXGFbY9qdgdZUm6LpXAAL9gD8W6c1wbGXYcD6CrpBvL => Ok(())

$ printf "%016x\n" 194969602
000000000b9f0002

$ git grep -C1 b9f_0002
programs/bpf/rust/invoke/src/lib.rs-                invoke(&invoked_instruction, accounts),
programs/bpf/rust/invoke/src/lib.rs:                Err(ProgramError::Custom(0x0b9f_0002))
programs/bpf/rust/invoke/src/lib.rs-            );
--
programs/bpf/rust/invoke/src/lib.rs-                invoke(&invoked_instruction, accounts),
programs/bpf/rust/invoke/src/lib.rs:                Err(ProgramError::Custom(0x0b9f_0002))
programs/bpf/rust/invoke/src/lib.rs-            );
--
programs/bpf_loader/src/lib.rs-    #[error("virtual machine failed to run the program to completion")]
programs/bpf_loader/src/lib.rs:    VirtualMachineFailedToRunProgram = 0x0b9f_0002,
programs/bpf_loader/src/lib.rs-}

[2020-09-10T07:29:17.868465223Z INFO  solana_runtime::message_processor] BPF program 4ckmDgGdxQoPDLUkDT3vHgSAkzA3QRdNq5ywwY4sUSJn failed: Unaligned pointer

[jackcmay]

Hmm, we want to enforce aligned pointers, probably need to gate this with the new loader

[ryoqun]

This is surpassed by #12176

@jackcmay Thanks for fixing this!