Added volatile qualifiers where needed.

Much less than expected as it turns out that there would be few benefits by using it extensively.
Pass emu_{freq,speed,granularity} by value instead of by reference.

Changing those while running will probably not be supported, so there is no need for a reference as of now.
Added -Werror build option.
m35fd : Do endianness fixes before any write to memory or to disk.