C99 compliant codebase

[ajaxvp]

The current ecc codebase is not compliant with C99, but I want it to be so that I might be able to compile ecc with itself one day. The only non-C99 features that the current codebase use are:

• Anonymous structs and unions (C11)
• Trailing comma removal in invocations of variadic function-like macros with zero varargs (GNU extension/C23)