Add --disable-arch-native build option

Add --disable-arch-native build option

The -march-native option is required by Clang 3.2 on some CPU
and produces better optimization in binaries by GCC.
But building inside a virtual machine environment has been found to
cause random Illegal Instruction errors due to mis-detection of CPU.

This option is added to permit selective disabling of teh preferred
default (which is to use the compiler flag when available).