Use _POSIX_C_SOURCE not _BSD_SOURCE.

_BSD_SOURCE has been deprecated (see bug). The manpage for printf
suggests that any _POSIX_C_SOURCE >= 200112L is also sufficient to bring
in the needed declarations and the bug reporter confirms that it's
sufficient for him.

https://code.google.com/p/chromium/issues/detail?id=419859

Change-Id: Ifc053f11c5aa1df35aae8e952d2c73a7f4599ec2
Reviewed-on: https://boringssl-review.googlesource.com/1890
Reviewed-by: Adam Langley <agl@google.com>

crypto/mem.c

diff --git a/crypto/mem.c b/crypto/mem.c
index 1eb97c9..b16b310 100644
--- a/crypto/mem.c
+++ b/crypto/mem.c
@@ -53,9 +53,7 @@
  * copied and put under another distribution licence
  * [including the GNU Public Licence.] */
 
-#if !defined(_BSD_SOURCE)
-#define _BSD_SOURCE /* needed for strdup, snprintf, vprintf etc */
-#endif
+#define _POSIX_C_SOURCE 201410L  /* needed for strdup, snprintf, vprintf etc */
 
 #include <openssl/mem.h>
 
@@ -66,6 +64,8 @@
 
 #if defined(OPENSSL_WINDOWS)
 #include <Windows.h>
+#else
+#include <strings.h>
 #endif