Fix f5314d15af - [Support] On Unix, let the CrashRecoveryContext return the signal code

This was causing bots to fail: http://green.lab.llvm.org/green/job/clang-stage1-RA/14828/consoleFull#6384962949ba4694-19c4-4d7e-bec5-911270d8a58c

llvm/unittests/Support/CrashRecoveryTest.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/Triple.h"
+#include "llvm/Config/config.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/CrashRecoveryContext.h"
@@ -23,6 +24,12 @@
 #include <windows.h>
 #endif
 
+#ifdef LLVM_ON_UNIX
+#ifdef HAVE_SIGNAL_H
+#include <signal.h>
+#endif
+#endif
+
 using namespace llvm;
 using namespace llvm::sys;