After partial revert of #208330 in #209928, the libcxx build started failing because of missing `<cstdint>` include required for `uintptr_t` declaration used only by code behind `ptrauth_calls` feature check. See https://lab.llvm.org/buildbot/#/builders/227/builds/3358 This patch adds the missing include. (cherry picked from commit 12e1c7f70f34d59c023d05d0fe2c228a4e9aac11)