[sanitizer] Fix build for new GLIBC msghdr/cmsghdr definition

GLIBC now follows POSIX [1] for both msghdr and cmsghdr definitions,
which means that msg_iovlen, msg_controllen, and cmsg_len are no
longer size_t but sockelen_t for 64-bits architectures. The final struct
size does not change, since paddings were added.

This patch fixes the build issue against GLIBC 2.24 socket.h header by
using the same definition for internal __sanitizer_msghdr and
__sanitizer_cmsghdr.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/

llvm-svn: 272008