feature_to_c.sh: Print help when passing no arguments

feature_to_c.sh: Print help when passing no arguments

I found that odd that passing no arguments to feature_to_c.sh produces
this:

$ ./feature_to_c.sh
./feature_to_c.sh: 23: shift: can't shift that many

but passing one argument shows the help:

$ ./feature_to_c.sh hello
Usage: ./feature_to_c.sh OUTPUTFILE INPUTFILE...

This patch changes the script to show the help in both cases.

gdb/ChangeLog:

	* features/feature_to_c.sh: Print the help when passing no
	argument.