Unbreak Mac build.

TBR=marja@chromium.org

Review URL: https://codereview.chromium.org/356153006

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22059 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/d8-posix.cc

@@ -4,6 +4,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <signal.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/select.h>