Allow libc++abi to be built without unwinder.

This CL adds a new compilation flags LIBCXXABI_USE_LLVM_UNWINDER
to specify whether the LLVM unwinder is enabled.  Besides, all
unwinder-specific code are guarded with this definition.

Now, libc++abi will be able to use the unwinding routine from libgcc
when LIBCXXABI_USE_LLVM_UNWINDER is disabled.


git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@226819 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed