Refactor logic to remove trailing CR/LF characters from strings

b654714 has reworked the way trailing CR/LF characters are removed from
strings.  This commit introduces a new routine in common/string.c and
refactors the code so as the logic is in a single place, mostly.

Author: Michael Paquier
Reviewed-by: Bruce Momjian
Discussion: https://postgr.es/m/20190801031820.GF29334@paquier.xyz

src/backend/libpq/be-secure-common.c

@@ -22,6 +22,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
+#include "common/string.h"
 #include "libpq/libpq.h"
 #include "storage/fd.h"
 
@@ -112,11 +113,8 @@ run_ssl_passphrase_command(const char *prompt, bool is_server_start, char *buf,
 		goto error;
 	}
 
-	/* strip trailing newline, including \r in case we're on Windows */
-	len = strlen(buf);
-	while (len > 0 && (buf[len - 1] == '\n' ||
-					   buf[len - 1] == '\r'))
-		buf[--len] = '\0';
+	/* strip trailing newline and carriage return */
+	len = pg_strip_crlf(buf);
 
 error:
 	pfree(command.data);