Work around missing include in afs/afs_daemons.c.

Gerrit 11642 assumes another patch from the same day that moves references
to d_alias out of afs/afs_daemons.c. Instead of cherrypicking that (and who
knows what else will be required) we duplicate the #define for d_alias here.
--- a/src/afs/afs_daemons.c
+++ b/src/afs/afs_daemons.c
@@ -27,6 +27,11 @@
 #if defined(AFS_CACHE_BYPASS)
 #include "afs/afs_bypasscache.h"
 #endif /* AFS_CACHE_BYPASS */
+
+#if defined(STRUCT_DENTRY_HAS_D_U_D_ALIAS)
+# define d_alias d_u.d_alias
+#endif
+
 /* background request queue size */
 afs_lock_t afs_xbrs;		/* lock for brs */
 static int brsInit = 0;
--- a/src/afs/LINUX/osi_vcache.c
+++ b/src/afs/LINUX/osi_vcache.c
@@ -13,6 +13,10 @@
 #include "afs/sysincludes.h"    /*Standard vendor system headers */
 #include "afsincludes.h"        /*AFS-based standard headers */
 
+#if defined(STRUCT_DENTRY_HAS_D_U_D_ALIAS)
+# define d_alias d_u.d_alias
+#endif
+
 int
 osi_TryEvictVCache(struct vcache *avc, int *slept, int defersleep) {
     int code;