[libc++] Re-exports from libc++abi are out of sync

[ldionne]

The set of libc++abi symbols we re-export from libc++ has gotten out of sync since libcxx/lib/libc++abi.exp wasn't updated. We should really generate the full set of symbols to re-export from libc++abi directly. Today we do it partially, for example exception symbols are re-exported via the cxxabi-reexports target, but other things like the typeinfo for fundamental types is hardcoded in libcxx/lib/libc++abi.exp.

[garymm]

I'm seeing this failure on MacOS with 19.1.7. Is it possible the same root cause? If so, is it expected that it's not fixed in 19.1.7?

Undefined symbols for architecture arm64:
  "std::__1::bad_expected_access<void>::what() const", referenced from:
      vtable for std::__1::bad_expected_access<starflate::detail::(anonymous namespace)::DecodeLitOrLenStatus> in libdecompress.a[2](decompress.o)
  "typeinfo for std::__1::bad_expected_access<void>", referenced from:
      typeinfo for std::__1::bad_expected_access<starflate::detail::(anonymous namespace)::DecodeLitOrLenStatus> in libdecompress.a[2](decompress.o)
  "vtable for std::__1::bad_expected_access<void>", referenced from:
      std::__1::bad_expected_access<void>::bad_expected_access[abi:ne190107]() in libdecompress.a[2](decompress.o)
   NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.