Fix CodeGen/AMDGPU/fcanonicalize-elimination.ll on FreeBSD 11.0

Summary:
On FreeBSD11.0 the FileCheck NOT string "1.0" will be matched by
`.amd_amdgpu_isa "amdgcn-unknown-freebsd11.0--gfx802"` at the end of the
file. Add a CHECK for that directive to avoid failing the test.

Reviewers: rampitec, kzhuravl

Reviewed By: rampitec, kzhuravl

Subscribers: emaste, kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, llvm-commits, krytarowski

Differential Revision: https://reviews.llvm.org/D39306

llvm-svn: 316616