[libc] Unit tests fail to build in fullbuild due to undefined symbols

[SchrodingerZhu]

Unit test objects are seeking for _Unwind_Resume.

[SchrodingerZhu]

This seems to be a clang bug since it is inside runtime build. From compiler-commands.json, -fno-exception and -fno-unwind-tables are specified, there should be no dependency to libunwind if I understand it correctly. cc @michaelrj-google

[michaelrj-google]

The actual library shouldn't have any dependency on libunwind or any other C++ runtime components, I would guess that the tests would be similar but the limitations on them aren't as strict.