configure: Add _FORTIFY_SOURCE=2

Add -D_FORTIFY_SOURCE=2 into CPPFLAGS if:

o it's not allready set in system headers
o optimalization is enabled

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
runltp: rework echo -n to printf POSIX-compliant

Signed-off-by: Anders Roxell <anders.roxell@linaro.org>