Index: include/llvm/Support/Signals.h
===================================================================
--- include/llvm/Support/Signals.h
+++ include/llvm/Support/Signals.h
@@ -39,6 +39,9 @@
   /// @brief Print a stack trace if a fatal signal occurs.
   void PrintStackTraceOnErrorSignal();
 
+  /// Disable all system dialog boxes that appear when the process crashes.
+  void DisableSystemDialogsOnCrash();
+
   /// \brief Print the stack trace using the given \c FILE object.
   void PrintStackTrace(FILE *);
 
Index: lib/Support/Unix/Signals.inc
===================================================================
--- lib/Support/Unix/Signals.inc
+++ lib/Support/Unix/Signals.inc
@@ -480,6 +480,8 @@
   PrintStackTrace(stderr);
 }
 
+void llvm::sys::DisableSystemDialogsOnCrash() {}
+
 /// PrintStackTraceOnErrorSignal - When an error signal (such as SIGABRT or
 /// SIGSEGV) is delivered to the process, print a stack trace and then exit.
 void llvm::sys::PrintStackTraceOnErrorSignal() {
Index: lib/Support/Windows/Signals.inc
===================================================================
--- lib/Support/Windows/Signals.inc
+++ lib/Support/Windows/Signals.inc
@@ -13,6 +13,7 @@
 
 #include "llvm/Support/FileSystem.h"
 #include <algorithm>
+#include <signal.h>
 #include <stdio.h>
 #include <vector>
 
@@ -165,7 +166,6 @@
 static std::vector<std::pair<void(*)(void*), void*> > *CallBacksToRun = 0;
 static bool RegisteredUnhandledExceptionFilter = false;
 static bool CleanupExecuted = false;
-static bool ExitOnUnhandledExceptions = false;
 static PTOP_LEVEL_EXCEPTION_FILTER OldFilter = NULL;
 
 // Windows creates a new thread to execute the console handler when an event
@@ -196,6 +196,12 @@
 
 #endif
 
+static void HandleAbort(int Sig) {
+  if (Sig == SIGABRT) {
+    LLVM_BUILTIN_TRAP;
+  }
+}
+
 static void RegisterHandler() {
 #if __MINGW32__ && !defined(__MINGW64_VERSION_MAJOR)
   // On MinGW.org, we need to load up the symbols explicitly, because the
@@ -226,17 +232,6 @@
   OldFilter = SetUnhandledExceptionFilter(LLVMUnhandledExceptionFilter);
   SetConsoleCtrlHandler(LLVMConsoleCtrlHandler, TRUE);
 
-  // Environment variable to disable any kind of crash dialog.
-  if (getenv("LLVM_DISABLE_CRASH_REPORT")) {
-#ifdef _MSC_VER
-    _CrtSetReportHook(AvoidMessageBoxHook);
-#endif
-    SetErrorMode(SEM_FAILCRITICALERRORS |
-                 SEM_NOGPFAULTERRORBOX |
-                 SEM_NOOPENFILEERRORBOX);
-    ExitOnUnhandledExceptions = true;
-  }
-
   // IMPORTANT NOTE: Caller must call LeaveCriticalSection(&CriticalSection) or
   // else multi-threading problems will ensue.
 }
@@ -276,9 +271,29 @@
   LeaveCriticalSection(&CriticalSection);
 }
 
+void sys::DisableSystemDialogsOnCrash() {
+  // Crash to stack trace handler on abort.
+  signal(SIGABRT, HandleAbort);
+
+  // The following functions are not reliably accessible on MinGW.
+#ifdef _MSC_VER
+  // We're already handling writing a "something went wrong" message.
+  _set_abort_behavior(0, _WRITE_ABORT_MSG);
+  // Disable Dr. Watson.
+  _set_abort_behavior(0, _CALL_REPORTFAULT);
+  _CrtSetReportHook(AvoidMessageBoxHook);
+#endif
+
+  // Disable standard error dialog box.
+  SetErrorMode(SEM_FAILCRITICALERRORS | SEM_NOGPFAULTERRORBOX |
+               SEM_NOOPENFILEERRORBOX);
+  _set_error_mode(_OUT_TO_STDERR);
+}
+
 /// PrintStackTraceOnErrorSignal - When an error signal (such as SIBABRT or
 /// SIGSEGV) is delivered to the process, print a stack trace and then exit.
 void sys::PrintStackTraceOnErrorSignal() {
+  DisableSystemDialogsOnCrash();
   RegisterHandler();
   LeaveCriticalSection(&CriticalSection);
 }
@@ -437,14 +452,7 @@
     fputc('\n', stderr);
   }
 
-  if (ExitOnUnhandledExceptions)
-    _exit(ep->ExceptionRecord->ExceptionCode);
-
-  // Allow dialog box to pop up allowing choice to start debugger.
-  if (OldFilter)
-    return (*OldFilter)(ep);
-  else
-    return EXCEPTION_CONTINUE_SEARCH;
+  _exit(ep->ExceptionRecord->ExceptionCode);
 }
 
 static BOOL WINAPI LLVMConsoleCtrlHandler(DWORD dwCtrlType) {