SPECIFIC(MUSL): there are no LFS64 symbol aliases on musl

See:
rust-lang/rust#106246
https://git.musl-libc.org/cgit/musl/commit/?id=246f1c811448f37a44b41cd8df8d0ef9736d95f4

Author: Jane Rachinger

src/basic/dirent-util.h

@@ -36,7 +36,8 @@ struct dirent *readdir_no_dot(DIR *dirp);
 /* Only if 64-bit off_t is enabled struct dirent + struct dirent64 are actually the same. We require this, and
  * we want them to be interchangeable to make getdents64() work, hence verify that. */
 assert_cc(_FILE_OFFSET_BITS == 64);
-#if HAVE_STRUCT_DIRENT64
+/* dirent64 is a macro on musl */
+#if HAVE_STRUCT_DIRENT64 && !defined(dirent64)
 assert_cc(sizeof(struct dirent) == sizeof(struct dirent64));
 assert_cc(offsetof(struct dirent, d_ino) == offsetof(struct dirent64, d_ino));
 assert_cc(sizeof_field(struct dirent, d_ino) == sizeof_field(struct dirent64, d_ino));