gh-989: Fix 32 bit x86 builds
gh-989: Fix 32 bit x86 builds

If building for 32 bit x86 target pass -march=i686 option to enable
atomic instructions.  i686 is usually the default arch but sometimes an
older one is selected (depends on gcc compile time configuration).

mejedi/tarantool,ocelot-inc/tarantool,ocelot-inc/tarantool,mejedi/tarantool,mejedi/tarantool,ocelot-inc/tarantool,rtsisyk/tarantool,mejedi/tarantool,rtsisyk/tarantool,ocelot-inc/tarantool,rtsisyk/tarantool,rtsisyk/tarantool