Make references to 'struct sigaction' compile under Solaris.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@19045 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/System/Unix/Program.cpp b/lib/System/Unix/Program.cpp
index 9469fff..18cbc33 100644
--- a/lib/System/Unix/Program.cpp
+++ b/lib/System/Unix/Program.cpp
@@ -19,6 +19,7 @@
 #include <llvm/Config/config.h>
 #include "Unix.h"
 #include <sys/stat.h>
+#include <signal.h>
 #include <fcntl.h>
 #ifdef HAVE_SYS_WAIT_H
 #include <sys/wait.h>