glcpp: Use printf instead of "echo -n" in glcpp-test

glcpp: Use printf instead of "echo -n" in glcpp-test

I noticed that with /bin/sh on Mac OS X, "echo -n" does not work as
desired, (it actually prints "-n" rather than suppressing the final
newline). There is a /bin/echo that could be used (it actually works)
instead of the builtin echo.

But I decided it's more robust to just use printf rather than
hardcoding /bin/echo into the script.