- Convert to option helpers
- Don't pretend MMX code can be used on amd64 [1]
- Lazy check if MMX is available on i386 [1]
[1] No changes in build behavior. --enable-mmx is a nop on non-i386 while
i386 still passes --disable-mmx by default unless CPUTYPE is set.
Approved by: mentors (implicit)