Again, only required for musl 1.2.4 but let's not make it harder on ourselves.
Upstream-URL: https://github.com/systemd/systemd/pull/27599

From d096e05c625ea825eb4d781216ded717b7f71cca Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Wed, 10 May 2023 01:47:13 +0100
Subject: [PATCH] dirent: conditionalize dirent assert based on dirent64
 existence

>=musl-1.2.4 doesn't define dirent64 and its LFS friends as its "native"
functions are already LFS-aware.

Check for dirent64 in meson.build and only assert if it exists.

Bug: https://bugs.gentoo.org/905900
Closes: https://github.com/systemd/systemd/pull/25809
--- a/meson.build
+++ b/meson.build
@@ -599,6 +599,7 @@ decl_headers = '''
 #   define _GNU_SOURCE 1
 # endif // _GNU_SOURCE
 #endif // 1
+#include <dirent.h>
 #include <uchar.h>
 #include <sys/mount.h>
 #include <sys/stat.h>
@@ -608,6 +609,7 @@ foreach decl : ['char16_t',
                 'char32_t',
                 'struct mount_attr',
                 'struct statx',
+                'struct dirent64',
                ]
 
         # We get -1 if the size cannot be determined
--- a/src/basic/dirent-util.h
+++ b/src/basic/dirent-util.h
@@ -39,6 +39,7 @@ struct dirent *readdir_no_dot(DIR *dirp);
 /* Only if 64bit 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
 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));
@@ -50,6 +51,7 @@ assert_cc(offsetof(struct dirent, d_type) == offsetof(struct dirent64, d_type));
 assert_cc(sizeof_field(struct dirent, d_type) == sizeof_field(struct dirent64, d_type));
 assert_cc(offsetof(struct dirent, d_name) == offsetof(struct dirent64, d_name));
 assert_cc(sizeof_field(struct dirent, d_name) == sizeof_field(struct dirent64, d_name));
+#endif
 
 #define FOREACH_DIRENT_IN_BUFFER(de, buf, sz)                           \
         for (void *_end = (uint8_t*) ({ (de) = (buf); }) + (sz);        \