Appease hosts without HAVE_BACKTRACE nor ENABLE_BACKTRACES.

  llvm/lib/Support/Signals.cpp:66:13: warning: unused function 'printSymbolizedStackTrace' [-Wunused-function]
  llvm/lib/Support/Signals.cpp:52:13: warning: function 'findModulesAndOffsets' has internal linkage but is not defined [-Wundefined-internal]

llvm-svn: 252418
diff --git a/llvm/lib/Support/Unix/Signals.inc b/llvm/lib/Support/Unix/Signals.inc
index fb1b400..d6d30bf 100644
--- a/llvm/lib/Support/Unix/Signals.inc
+++ b/llvm/lib/Support/Unix/Signals.inc
@@ -306,6 +306,13 @@
   return false;
 }
 #endif
+#else
+static bool findModulesAndOffsets(void **StackTrace, int Depth,
+                                  const char **Modules, intptr_t *Offsets,
+                                  const char *MainExecutableName,
+                                  StringSaver &StrPool) {
+  return false;
+}
 #endif // defined(HAVE_BACKTRACE) && defined(ENABLE_BACKTRACES)
 
 // PrintStackTrace - In the case of a program crash or fault, print out a stack