Add a description of DCHUNK_SIZE to the Makefile
Turn off Extra Runtime crash Analysis by Default

Those that want it enabled will be capable of turning it on.
Add CPPFLAGS, LDFLAGS to gcc build and harden

CPPFLAGS is a typical way to add -D_FORTIFY_SOURCE=2

-fPIE and -fstack-protector-all are added to CDEBUGFLAGS

LDFLAGS allows us to use '-pie -Wl,-z,relro -Wl,-z,now'
hardening options as well as '-Wl,-O1 -Wl,--sort-common'
linker optimisations.