Unskip statx and statx_timestamp tests on Linux

The mentioned issues with `#include` no longer seem to happen, so start testing these again.

Author: tgross35

libc-test/build.rs

@@ -3989,12 +3989,6 @@ fn test_linux(target: &str) {
  // glibcs (see https://github.com/rust-lang/libc/issues/1410)
  "ucontext_t" if gnu => true,
 
- // FIXME(linux): Somehow we cannot include headers correctly in glibc 2.30.
- // So let's ignore for now and re-visit later.
- // Probably related: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91085
- "statx" => true,
- "statx_timestamp" => true,
-
  // On Linux, the type of `ut_exit` field of struct `utmpx`
  // can be an anonymous struct, so an extra struct,
  // which is absent in musl, has to be defined.