[regress/agent-ptrace.sh] sh doesn't like "if ! shell_function; then".
diff --git a/regress/agent-ptrace.sh b/regress/agent-ptrace.sh
index b9d86a2..cd9c002 100644
--- a/regress/agent-ptrace.sh
+++ b/regress/agent-ptrace.sh
@@ -12,7 +12,9 @@
 	esac
 fi
 
-if ! have_prog gdb ; then
+if have_prog gdb ; then
+	: ok
+else
 	echo "skipped (gdb not found)"
 	exit 0
 fi