Makefile:Add GCC flag -fno-delete-null-pointer-checks

-fdelete-null-pointer-checks flag controls global dataflow analyses and
eliminate useless checks for null pointers; It assume that if a pointer is
checked after it has already been dereferenced, it cannot be null.
This flag is enabled by default.

gcc v4.9 has more optimizations added to this option. Hence it is very
aggressive with GCC v4.9 series. Add -fno-delete-null-pointer-checks to
disable the optimization

Signed-off-by: Rohit Dharmakan <rohitarulraj@freescale.com>
Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>