Generate fmgr prototypes automatically

Gen_fmgrtab.pl creates a new file fmgrprotos.h, which contains
prototypes for all functions registered in pg_proc.h.  This avoids
having to manually maintain these prototypes across a random variety of
header files.  It also automatically enforces a correct function
signature, and since there are warnings about missing prototypes, it
will detect functions that are defined but not registered in
pg_proc.h (or otherwise used).

Reviewed-by: Pavel Stehule <pavel.stehule@gmail.com>

src/backend/access/hash/hashfunc.c

@@ -27,7 +27,17 @@
 #include "postgres.h"
 
 #include "access/hash.h"
+#include "utils/builtins.h"
 
+/*
+ * Datatype-specific hash functions.
+ *
+ * These support both hash indexes and hash joins.
+ *
+ * NOTE: some of these are also used by catcache operations, without
+ * any direct connection to hash indexes.  Also, the common hash_any
+ * routine is also used by dynahash tables.
+ */
 
 /* Note: this is used for both "char" and boolean datatypes */
 Datum