We need to case this on sizeof(time_t), not sizeof(void*).

--- dovecot-2.3.20/src/lib-index/mail-cache-fields.c.old	2023-02-22 08:01:49.420556821 +0000
+++ dovecot-2.3.20/src/lib-index/mail-cache-fields.c	2023-02-23 09:45:11.417417626 +0000
@@ -529,7 +529,7 @@
 copy_to_buf_last_used(struct mail_cache *cache, buffer_t *dest, bool add_new)
 {
 	size_t offset = offsetof(struct mail_cache_field, last_used);
-#if defined(WORDS_BIGENDIAN) && SIZEOF_VOID_P == 8
+#if defined(WORDS_BIGENDIAN) && TIME_T_MAX_BITS > 32
 	/* 64bit time_t with big endian CPUs: copy the last 32 bits instead of
 	   the first 32 bits (that are always 0). The 32 bits are enough until
 	   year 2106, so we're not in a hurry to use 64 bits on disk. */