Use .cfi_sections to put the unwind info in .debug_frame when possible. With

Use .cfi_sections to put the unwind info in .debug_frame when possible. With
this clang will use .debug_frame in, for example,
clang -g -c -m32 test.c
This matches gcc's behaviour. It looks like .debug_frame is a bit bigger
than .eh_frame, but has the big advantage of not being allocated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131140 91177308-0d34-0410-b5e6-96231b3b80d8