Native code support for armv6 on FreeBSD10

* configure accepts armv6/freebsd for native code compilation
* 'as' and 'aspp' map to 'cc -c'
* new section in arm.S to configure SYS_freebsd for armv6+softfp
* arch/arm.ml maps Sys.config="freebsd" to EABI

Tested on FreeBSD RELEASE/10 on Raspberry PI.