Fix NaCl build.

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>

crypto/bio/bio_test.c

@@ -12,7 +12,9 @@
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
 
+#if !defined(_POSIX_C_SOURCE)
 #define _POSIX_C_SOURCE 201410L
+#endif
 
 #include <openssl/base.h>
 

crypto/lhash/lhash_test.c

@@ -12,7 +12,9 @@
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
 
+#if !defined(_POSIX_C_SOURCE)
 #define _POSIX_C_SOURCE 201410L
+#endif
 
 #include <openssl/crypto.h>
 #include <openssl/lhash.h>

crypto/mem.c

@@ -53,7 +53,9 @@
  * copied and put under another distribution licence
  * [including the GNU Public Licence.] */
 
+#if !defined(_POSIX_C_SOURCE)
 #define _POSIX_C_SOURCE 201410L  /* needed for strdup, snprintf, vprintf etc */
+#endif
 
 #include <openssl/mem.h>
 

crypto/time_support.c

@@ -55,7 +55,9 @@
  * (eay@cryptsoft.com).  This product includes software written by Tim
  * Hudson (tjh@cryptsoft.com). */
 
+#if !defined(_POSIX_C_SOURCE)
 #define _POSIX_C_SOURCE 201410L  /* for gmtime_r */
+#endif
 
 #include <openssl/time_support.h>