dccp exports are tied to glibc on linux #3132
Description
the various DCCP_ exports such as DCCP_SOCKOPT_SERVICE are tied to linux/gnu (or android). that means they are not present on linux/musl.
however, these defines don't come from the libc. for instance:
#include <sys/socket.h>
#include <stdio.h>
int main(void) {
printf("%d\n", DCCP_SOCKOPT_SERVICE);
}fails to compile on either glibc or musl. this is because they actually come from <linux/dccp.h>.
since they come from the kernel headers, they should also be present in linux/musl/mod.rs (or wherever they are meant to be defined here.)
(mostly an upstream version of a downstream bug report: rust-lang/socket2#405)