Add freeze-stdlib compile flag

Cargo.toml

@@ -17,6 +17,7 @@ path = "./benchmarks/bench.rs"
 [features]
 default = ["rustpython-vm/use-proc-macro-hack"]
 flame-it = ["rustpython-vm/flame-it", "flame", "flamescope"]
+freeze-stdlib = ["rustpython-vm/freeze-stdlib"]
 
 [dependencies]
 log="0.4.1"

vm/Cargo.toml

@@ -13,6 +13,7 @@ default = ["rustpython-parser", "rustpython-compiler", "use-proc-macro-hack"]
 vm-tracing-logging = []
 flame-it = ["flame", "flamer"]
 use-proc-macro-hack = ["proc-macro-hack", "rustpython-derive/proc-macro-hack"]
+freeze-stdlib = []
 
 [dependencies]
 # Crypto: