Add boolean to PrintStackTraceOnErrorSignal to disable crash reporting.

The current crash reporting on Mac OS is only disabled via an environment variable.
This adds a boolean (default false) which can also disable crash reporting.

The only client right now is the unittests which don't ever want crash reporting, but do want to detect killed programs.

Reduces the time to run the APFloat unittests on my machine from

[----------] 47 tests from APFloatTest (51250 ms total)

to

[----------] 47 tests from APFloatTest (765 ms total)

Reviewed by Reid Kleckner and Justin Bogner

llvm-svn: 234353
diff --git a/llvm/lib/Support/Windows/Signals.inc b/llvm/lib/Support/Windows/Signals.inc
index de6bf1c..f070111 100644
--- a/llvm/lib/Support/Windows/Signals.inc
+++ b/llvm/lib/Support/Windows/Signals.inc
@@ -389,7 +389,7 @@
 
 /// 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() {
+void sys::PrintStackTraceOnErrorSignal(bool DisableCrashReporting) {
   DisableSystemDialogsOnCrash();
   RegisterHandler();
   LeaveCriticalSection(&CriticalSection);