Bump bpf-tools to v1.20

- Fix C standard library to include only reentrant versions of functions
- Use a version of solana_rbpf with fixed relocations handling
- Add a test of using C standard library functions in on-chain program

programs/bpf/tests/programs.rs

@@ -441,6 +441,7 @@ fn test_program_bpf_sanity() {
             ("sanity++", true),
             ("secp256k1_recover", true),
             ("sha", true),
+            ("stdlib", true),
             ("struct_pass", true),
             ("struct_ret", true),
         ]);