test,static-destruct: Use retain attribute to prevent linker garbage collection

Fixes: #21847

src/basic/static-destruct.h

@@ -24,12 +24,16 @@ typedef struct StaticDestructor {
                 typeof(variable) *q = p;                                \
                 func(q);                                                \
         }                                                               \
+        /* Older compilers don't know retain attribute. */              \
+        _Pragma("GCC diagnostic ignored \"-Wattributes\"")              \
         /* The actual destructor structure we place in a special section to find it */ \
         _section_("SYSTEMD_STATIC_DESTRUCT")                            \
         /* We pick pointer alignment, since that is apparently what gcc does for static variables */ \
         _alignptr_                                                      \
         /* Make sure this is not dropped from the image because not explicitly referenced */ \
         _used_                                                          \
+        /* Prevent linker from garbage collection. */                   \
+        _retain_                                                        \
         /* Make sure that AddressSanitizer doesn't pad this variable: we want everything in this section
          * packed next to each other so that we can enumerate it. */     \
         _variable_no_sanitize_address_                                  \