They're not thread-safe so they should not be used in libcurl code.
Explictly enabled when deemed necessary and in examples and tests
Reviewed-by: Nicolas Sterchele
Closes#5732
- Stick to a single unified way to use structs
- Make checksrc complain on 'typedef struct {'
- Allow them in tests, public headers and examples
- Let MD4_CTX, MD5_CTX, and SHA256_CTX typedefs remain as they actually
typedef different types/structs depending on build conditions.
Closes#5338