Reland "[CMake][libunwind] Use -nodefaultlibs for CMake checks"

This is a reland of commit r299796.

Turned out that we need gcc_s or compiler-rt on ARM when checking
the support for -funwind-tables which creates a dependency on
__aeabi_unwind_cpp_pr0 symbol that's provided by the compiler
runtime.

Differential Revision: https://reviews.llvm.org/D31858

llvm-svn: 300020