shared: add DLOPEN_* wrapper macros that stamp .note.dlopen on callers

This macro emits an SD_ELF_NOTE_DLOPEN note so that calling sites,
and not just libsystemd-shared, get the ELF stamped with the notes
documenting the dependency. Currently most of the dlopen notes end
up in libsystemd-shared, and executables have no way to document
the optional dependencies they need. With this new macro, this
issue can be fixed.

Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>

src/basic/locale-util.c

@@ -39,11 +39,7 @@ int dlopen_libintl(int log_level) {
 #else
         static void *libintl_dl = NULL;
 
-        SD_ELF_NOTE_DLOPEN(
-                        "intl",
-                        "Support for message translation via gettext",
-                        SD_ELF_NOTE_DLOPEN_PRIORITY_SUGGESTED,
-                        "libintl.so.8");
+        LIBINTL_NOTE(SD_ELF_NOTE_DLOPEN_PRIORITY_SUGGESTED);
 
         return dlopen_many_sym_or_warn(
                         &libintl_dl,

src/basic/locale-util.h

@@ -4,6 +4,8 @@
 #include <libintl.h>    /* IWYU pragma: export */
 #include <locale.h>     /* IWYU pragma: export */
 
+#include "sd-dlopen.h"  /* IWYU pragma: export */
+
 #include "basic-forward.h"
 #include "dlfcn-util.h"
 
@@ -14,6 +16,22 @@ extern DLSYM_PROTOTYPE(dgettext) __attribute__((format_arg(2)));
 
 int dlopen_libintl(int log_level);
 
+#ifdef __GLIBC__
+#define DLOPEN_LIBINTL(log_level, priority) dlopen_libintl(log_level)
+#else
+#define LIBINTL_NOTE(priority)                                          \
+        SD_ELF_NOTE_DLOPEN("intl",                                      \
+                           "Support for message translation via gettext", \
+                           priority,                                    \
+                           "libintl.so.8")
+
+#define DLOPEN_LIBINTL(log_level, priority)                             \
+        ({                                                              \
+                LIBINTL_NOTE(priority);                                 \
+                dlopen_libintl(log_level);                              \
+        })
+#endif
+
 typedef enum LocaleVariable {
         /* We don't list LC_ALL here on purpose. People should be
          * using LANG instead. */