Indicate that we print the non-symbolized stack trace and information about how to get it symbolized

[mehdi_amini]

Summary

Most users of LLVM tools hit the raw traces and don't know how to get LLVM to
symbolize automatically for them.

[MaskRay]

Good idea. I only got to know this after I read the source code. Many people probably have the same confusion.

Indicate that we print the non-symbolized stack trace and information about how to get it symbolized

Perhaps reword this a bit, like "Hint how to get a symbolized stack trace if llvm-symbolizer is not found"?

llvm/lib/Support/Unix/Signals.inc

#endif
   if (!depth)
     return;
   // If "Depth" is not provided by the caller, use the return value of
   // backtrace() for printing a symbolized stack trace.
   if (!Depth)
     Depth = depth;
   if (printSymbolizedStackTrace(Argv0, StackTrace, Depth, OS))
     return;
+  OS << "Stack dump without symbol names (ensure you have llvm-symbolizer in "
+        "your PATH or set the environment var `LLVM_SYMBOLIZER_PATH` to point "
+        "to it):\n";
 #if HAVE_DLFCN_H && HAVE_DLADDR
   int width = 0;
   for (int i = 0; i < depth; ++i) {
     Dl_info dlinfo;
     dladdr(StackTrace[i], &dlinfo);
     const char* name = strrchr(dlinfo.dli_fname, '/');
 
     int nwidth;