fix build on cygwin
Cygwin has dlfcn.h, but no Dl_info

llvm-svn: 283427
diff --git a/llvm/lib/Support/Unix/Signals.inc b/llvm/lib/Support/Unix/Signals.inc
index 46b640a..9752b70 100644
--- a/llvm/lib/Support/Unix/Signals.inc
+++ b/llvm/lib/Support/Unix/Signals.inc
@@ -412,7 +412,7 @@
 
   if (printSymbolizedStackTrace(Argv0, StackTrace, depth, OS))
     return;
-#if HAVE_DLFCN_H && __GNUG__
+#if HAVE_DLFCN_H && __GNUG__ && !defined(__CYGWIN__)
   int width = 0;
   for (int i = 0; i < depth; ++i) {
     Dl_info dlinfo;