Make libc++abi C++17 ready

libc++abi used to fail to compile in C++17 mode, as it touches
std::unexpected, which is removed in C++17.

This CL adds _LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS macro
to all libc++abi files, so that libc++ provides missing std::unexpected
even in C++17.

Bug: 752720
Change-Id: Ib7cc2e350ae9bcd373cd9b4ea91ee4dcb85a0b6a
1 file changed