[lldb] Add Python bindings to print stack traces on crashes.

As noticed in D87637, when LLDB crashes, we only print stack traces if
LLDB is directly executed, not when used via Python bindings. Enabling
this by default may be undesirable (libraries shouldn't be messing with
signal handlers), so make this an explicit opt-in.

I "commandeered" this patch from Jordan Rupprecht who put this up for
review originally.

Differential revision: https://reviews.llvm.org/D91835

lldb/bindings/interface/SBDebugger.i

@@ -141,6 +141,8 @@ public:
     static SBError
     InitializeWithErrorHandling();
 
+    static void PrintStackTraceOnError();
+
     static void
     Terminate();
 

lldb/include/lldb/API/SBDebugger.h

@@ -92,6 +92,8 @@ public:
 
   static lldb::SBError InitializeWithErrorHandling();
 
+  static void PrintStackTraceOnError();
+
   static void Terminate();
 
   // Deprecated, use the one that takes a source_init_files bool.

lldb/packages/Python/lldbsuite/test/dotest.py

@@ -880,6 +880,7 @@ def run_suite():
 
     import lldb
     lldb.SBDebugger.Initialize()
+    lldb.SBDebugger.PrintStackTraceOnError()
 
     checkLibcxxSupport()
     checkLibstdcxxSupport()

lldb/source/API/SBDebugger.cpp

@@ -57,6 +57,8 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/DynamicLibrary.h"
 #include "llvm/Support/ManagedStatic.h"
+#include "llvm/Support/PrettyStackTrace.h"
+#include "llvm/Support/Signals.h"
 
 using namespace lldb;
 using namespace lldb_private;
@@ -206,6 +208,15 @@ lldb::SBError SBDebugger::InitializeWithErrorHandling() {
   return error;
 }
 
+void SBDebugger::PrintStackTraceOnError() {
+  LLDB_INSTRUMENT();
+
+  llvm::EnablePrettyStackTrace();
+  // We don't have a meaningful argv[0] to use, so use "SBDebugger" as a
+  // substitute.
+  llvm::sys::PrintStackTraceOnErrorSignal("SBDebugger");
+}
+
 void SBDebugger::Terminate() {
   LLDB_INSTRUMENT();