[test-release.sh] Add -no-libunwind to disable it on targets that don't support it.

Summary:
Mips doesn't implement unw_getcontext() or libunwind::Registers_*::jumpto() yet
so we must disable libunwind for this release.

Reviewers: hans

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D11563

llvm-svn: 243633