src: print backtrace on fatal error

Print a C backtrace on fatal errors to make it easier to debug issues
like nodejs#6727.

node.gyp

@@ -402,6 +402,7 @@
 
         [ 'OS=="win"', {
           'sources': [
+            'src/backtrace_win32.cc',
             'src/res/node.rc',
           ],
           'defines!': [
@@ -416,6 +417,7 @@
           'libraries': [ '-lpsapi.lib' ]
         }, { # POSIX
           'defines': [ '__POSIX__' ],
+          'sources': [ 'src/backtrace_posix.cc' ],
         }],
         [ 'OS=="mac"', {
           # linking Corefoundation is needed since certain OSX debugging tools

src/backtrace_posix.cc

@@ -0,0 +1,36 @@
+#include "node.h"
+
+#include <cxxabi.h>
+#include <dlfcn.h>
+#include <execinfo.h>
+#include <stdio.h>
+
+namespace node {
+
+void DumpBacktrace(FILE* fp) {
+  void* frames[256];
+  const int size = backtrace(frames, arraysize(frames));
+  if (size <= 0) {
+    return;
+  }
+  for (int i = 1; i < size; i += 1) {
+    const void* frame = frames[i];
+    fprintf(fp, "%2d: ", i);
+    Dl_info info;
+    const bool have_info = dladdr(frame, &info);
+    if (!have_info || info.dli_sname == nullptr) {
+      fprintf(fp, "%p", frame);
+    } else if (char* demangled = abi::__cxa_demangle(info.dli_sname, 0, 0, 0)) {
+      fprintf(fp, "%s", demangled);
+      free(demangled);
+    } else {
+      fprintf(fp, "%s", info.dli_sname);
+    }
+    if (have_info && info.dli_fname != nullptr) {
+      fprintf(fp, " [%s]", info.dli_fname);
+    }
+    fprintf(fp, "\n");
+  }
+}
+
+}  // namespace node

src/backtrace_win32.cc

@@ -0,0 +1,8 @@
+#include "node.h"
+
+namespace node {
+
+void DumpBacktrace(FILE* fp) {
+}
+
+}  // namespace node

src/node.cc

@@ -2383,6 +2383,7 @@ static void OnFatalError(const char* location, const char* message) {
   } else {
     PrintErrorString("FATAL ERROR: %s\n", message);
   }
+  DumpBacktrace(stderr);
   fflush(stderr);
   ABORT();
 }

src/node_internals.h

@@ -7,6 +7,7 @@
 #include "uv.h"
 #include "v8.h"
 
+#include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
 
@@ -132,6 +133,8 @@ void AppendExceptionLine(Environment* env,
                          v8::Local<v8::Value> er,
                          v8::Local<v8::Message> message);
 
+void DumpBacktrace(FILE* fp);
+
 NO_RETURN void FatalError(const char* location, const char* message);
 
 v8::Local<v8::Value> BuildStatsObject(Environment* env, const uv_stat_t* s);