translate-c: enum constants can have incorrect type

[ehaas]

The following code translates incorrectly due to the underlying int type of an enum type being different from the int type of an enum constant (in the below C code, a variable of type foo would have an underlying representation of unsigned, but the enum constant bar has type int). In the translated Zig code, bar has type c_uint since that is the return type of @enumToInt(enum_foo.bar); it should be c_int

This bug was revealed (but not caused by) #8394, I believe the fix is to coerce enum redecls to the correct int type.

enum foo { bar };
int main(void) {
   char c = bar;
}

pub const enum_foo = extern enum(c_uint) {
    bar,
    _,
};
pub const bar = @enumToInt(enum_foo.bar);
pub export fn main() c_int {
    var c: u8 = @bitCast(u8, @truncate(i8, bar));
    return 0;
}

./enums.zig:8:44: error: expected signed integer type, found 'c_uint'
    var c: u8 = @bitCast(u8, @truncate(i8, bar));
                                           ^
./enums.zig:8:30: note: referenced here
    var c: u8 = @bitCast(u8, @truncate(i8, bar));
                             ^

[LemonBoy]

The long-term plan was to stop translating C enumeration types into Zig's extern enum and instead emit each single value as a standalone constant of suitable type.

The idea was proposed and approved here.