use __progname on BSD.

Index: clients/touch-calibrator.c
--- clients/touch-calibrator.c.orig
+++ clients/touch-calibrator.c
@@ -36,6 +36,8 @@
 #include <getopt.h>
 #include <errno.h>
 
+extern char *__progname;
+
 #include <wayland-client.h>
 
 #include "clients/window.h"
@@ -871,7 +873,7 @@ pr_err(const char *fmt, ...)
 	va_list argp;
 
 	va_start(argp, fmt);
-	fprintf(stderr, "%s error: ", program_invocation_short_name);
+	fprintf(stderr, "%s error: ", __progname);
 	vfprintf(stderr, fmt, argp);
 	va_end(argp);
 }
@@ -883,7 +885,7 @@ help(void)
 		"a Wayland compositor by\n"
 		"having the user touch points on the screen.\n\n");
 	fprintf(stderr, "Usage: %s [options...] name\n\n",
-		program_invocation_short_name);
+		__progname);
 	fprintf(stderr,
 		"Where 'name' can be a touch device sys path or a head name.\n"
 		"If 'name' is not given, all devices available for "
