Replace perror with custom postgres logging

perror() is not used in postgres anymore out of policy, this replaces
the final callsites with the custom postgres logging framework.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/89B00F63-40F7-4D82-8353-DC9CABBAC1D1@yesql.se

src/common/exec.c

@@ -378,7 +378,8 @@ pipe_read_line(char *cmd)
 	errno = 0;
 	if ((pipe_cmd = popen(cmd, "r")) == NULL)
 	{
-		perror("popen failure");
+		log_error(errcode(ERRCODE_SYSTEM_ERROR),
+				  _("could not execute command \"%s\": %m"), cmd);
 		return NULL;
 	}