runtime: use SYSCALL on FreeBSD

[bradfitz]

Go 1.2 and Go 1.3 require FreeBSD kernels be built with COMPAT_FREEBSD32 due to a
FreeBSD kernel bug with SYSCALL.  Go is currently using INT $0x80 as a workaround.

This bug is about switching back to SYSCALL, once modern FreeBSD kernels with the fix
are prevalent.

See issue #7056 for background.

[davecheney]

Comment 1:

SGTM.

[rsc]

Comment 2:

FreeBSD 10 was buggy. FreeBSD 11 just came out. Let's give it another release cycle.

Labels changed: added release-go1.5, removed release-go1.4.

[sean-]

Is this a bug with the entire branch or is this specific to a particular release?

[minux]

This is fixed. See #9627.