Pin libc++ until Skia is able to build with ToT abseil. ANGLE pins abseil-cpp until https://skbug.com/330350366 is resolved. Therefore ANGLE's abseil-cpp uses old DEF files, which can't be kept in sync with new libc++, e.g. here: https://chromium-review.googlesource.com/c/angle/angle/+/5391204/1 Bug: angleproject:8555 Change-Id: Ib61a80136e389ffbd67c7c378a5c8d9c2659be55 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5397577 Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Solti Ho <solti@google.com> Commit-Queue: Solti Ho <solti@google.com> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Auto-Submit: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Yuxin Hu <yuxinhu@google.com>