This change updates make_distrib.py to link in all of libc++ and libc++abi from the Chromium build when generating cef_sandbox.a. This increases the size of the release build of cef_sandbox.a from about 0.5 MB to about 2.0 MB, but it ensures that no C++ symbols are imported by the archive.
Linking cef_sandbox.a with an incompatible C++ library prior to this change could cause undefined behavior in the resulting binary.
To make sure that we do not regress this fix, this change also updates make_distrib.py to verify that no C++ symbols are imported by cef_sandbox.a after it is generated (in a way similar to the way we verify that cef_sandbox.a exports the correct symbols).
