libpq: Move pg_cancel to fe-cancel.c

No other files need to access this struct, so there is no need to have
its definition in a header file.

Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/202403061822.spfzqbf7dsgg@alvherre.pgsql

src/interfaces/libpq/fe-cancel.c

@@ -21,6 +21,26 @@
 #include "libpq-int.h"
 #include "port/pg_bswap.h"
 
+
+/*
+ * pg_cancel (backing struct for PGcancel) stores all data necessary to send a
+ * cancel request.
+ */
+struct pg_cancel
+{
+	SockAddr	raddr;			/* Remote address */
+	int			be_pid;			/* PID of to-be-canceled backend */
+	int			be_key;			/* cancel key of to-be-canceled backend */
+	int			pgtcp_user_timeout; /* tcp user timeout */
+	int			keepalives;		/* use TCP keepalives? */
+	int			keepalives_idle;	/* time between TCP keepalives */
+	int			keepalives_interval;	/* time between TCP keepalive
+										 * retransmits */
+	int			keepalives_count;	/* maximum number of TCP keepalive
+									 * retransmits */
+};
+
+
 /*
  * PQgetCancel: get a PGcancel structure corresponding to a connection.
  *

src/interfaces/libpq/libpq-int.h

@@ -621,24 +621,6 @@ struct pg_conn
 	PQExpBufferData workBuffer; /* expansible string */
 };
 
-/* PGcancel stores all data necessary to cancel a connection. A copy of this
- * data is required to safely cancel a connection running on a different
- * thread.
- */
-struct pg_cancel
-{
-	SockAddr	raddr;			/* Remote address */
-	int			be_pid;			/* PID of backend --- needed for cancels */
-	int			be_key;			/* key of backend --- needed for cancels */
-	int			pgtcp_user_timeout; /* tcp user timeout */
-	int			keepalives;		/* use TCP keepalives? */
-	int			keepalives_idle;	/* time between TCP keepalives */
-	int			keepalives_interval;	/* time between TCP keepalive
-										 * retransmits */
-	int			keepalives_count;	/* maximum number of TCP keepalive
-									 * retransmits */
-};
-
 
 /* String descriptions of the ExecStatusTypes.
  * direct use of this array is deprecated; call PQresStatus() instead.