llvm-cxxfilt: add missing includes from previous change

llvm-svn: 292580
diff --git a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
index 16dd37f..6076a63 100644
--- a/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
+++ b/llvm/tools/llvm-cxxfilt/llvm-cxxfilt.cpp
@@ -9,6 +9,8 @@
 
 #include "llvm/Demangle/Demangle.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/PrettyStackTrace.h"
+#include "llvm/Support/Signals.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstdlib>
 #include <iostream>