test: linux: Unskip ip_mreqn and hwtstamp_config

The reason these failed in the first place was unclear, but they now pass. Closes: #1558

Author: tgross35

libc-test/build.rs

@@ -3942,11 +3942,6 @@ fn test_linux(target: &str) {
  return true;
  }
 
- // FIXME(#1558): passing by value corrupts the value for reasons not understood.
- if (gnu && sparc64) && (ty == "ip_mreqn" || ty == "hwtstamp_config") {
- return true;
- }
-
  // FIXME(rust-lang/rust#43894): pass by value for structs that are not an even 32/64 bits
  // on big-endian systems corrupts the value for unknown reasons.
  if (sparc64 || ppc || ppc64 || s390x)