bpo-39943: Clean up marshal.c. (GH-19236)

* Add consts.
* Remove redundant casts and checks.
* Use concrete C API macros.
* Avoid raising and silencing OverflowError for ints.

Serhiy Storchaka committed 6y ago

2c003eff8fef430f1876adf88e466bcfcbd0cc9e

Parent: a9f9687

Committed by GitHub <noreply@github.com> on 3/31/2020, 8:23:21 PM