build: set RTE_ARCH_64 based on pointer size

build: set RTE_ARCH_64 based on pointer size

Rather than relying on the target machine architecture, use the
size of a pointer from the compiler to determine if we are 64-bits
or not. This allows correct behaviour when you pass -m32 as a compile
option. It also allows us to use this value repeatedly throughout the
repo rather than continually testing for the sizeof(void*).

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Luca Boccassi <bluca@debian.org>
Acked-by: Luca Boccassi <bluca@debian.org>