Include signal.h instead of replicating typedef to avoid errors from...

Include signal.h instead of replicating typedef to avoid errors from redefining it...provides better compat with non-Ubuntu distros

indra/llcommon/llapp.h

@@ -38,7 +38,7 @@ typedef LLAtomic32<U32> LLAtomicU32;
 class LLErrorThread;
 class LLLiveFile;
 #if LL_LINUX
-typedef struct siginfo siginfo_t;
+#include <signal.h>
 #endif
 
 typedef void (*LLAppErrorHandler)();