add a knob to turn off PrettyStackTrace globally.  Patch by Zoltan
Varga!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75897 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/PrettyStackTrace.cpp b/lib/Support/PrettyStackTrace.cpp
index 14290a1..536d9b0 100644
--- a/lib/Support/PrettyStackTrace.cpp
+++ b/lib/Support/PrettyStackTrace.cpp
@@ -19,6 +19,10 @@
 #include "llvm/ADT/SmallString.h"
 using namespace llvm;
 
+namespace llvm {
+  bool DisablePrettyStackTrace = false;
+}
+
 // FIXME: This should be thread local when llvm supports threads.
 static sys::ThreadLocal<const PrettyStackTraceEntry> PrettyStackTraceHead;
 
@@ -75,7 +79,8 @@
 }
 
 static bool RegisterCrashPrinter() {
-  sys::AddSignalHandler(CrashHandler, 0);
+  if (!DisablePrettyStackTrace)
+    sys::AddSignalHandler(CrashHandler, 0);
   return false;
 }