ID:355 - Add macros and #include and reduce number of warnings

Commit adds macros and #include in order to bring down the number of `warning:
implicit declaration of function 'X' [-Wimplicit-function-declaration]`
warnings.

lib/log.c

@@ -29,6 +29,9 @@
  * LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE,
  * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
  */
+#define _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500 || \
+	_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || \
+	/* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
 
 #include <unistd.h>
 #include <stdio.h>