NaCl defines _POSIX_C_SOURCE on the command line for some reason, thus we have to be defensive about defining it. Change-Id: Icbc8afcb1ac0e0ca23b788b11ea911c3f55a8b7f Reviewed-on: https://boringssl-review.googlesource.com/1891 Reviewed-by: David Benjamin <davidben@chromium.org> Reviewed-by: Adam Langley <agl@google.com>kris/onging/CECPQ3_patch15