build: use POSITION_INDEPENDENT_CODE instead of -fPIC

Rather than hardcode the flag and check if the compiler supports it, use
the CMake property to get the right flag spelling for the compiler.
This makes it generally more portable.

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@314834 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed