Always use --eh-frame-hdr on FreeBSD, even for -static

FreeBSD uses LLVM's libunwind on FreeBSD/arm64 today (and is expected to
use it more widely in the future), and it requires the EH frame segment
in static binaries.

This is the same as r203742 for NetBSD.

Differential Revision:	http://reviews.llvm.org/D19029

llvm-svn: 266123