Index: lib/Support/PrettyStackTrace.cpp
===================================================================
--- lib/Support/PrettyStackTrace.cpp
+++ lib/Support/PrettyStackTrace.cpp
@@ -32,13 +32,16 @@
 // thread-local variable. Some day, we should be able to use a limited subset
 // of C++11's thread_local, but compilers aren't up for it today.
 // FIXME: This should be moved to a Compiler.h abstraction.
+#if ENABLE_BACKTRACE
 #ifdef _MSC_VER // MSVC supports this with a __declspec.
 static __declspec(thread) const PrettyStackTraceEntry
     *PrettyStackTraceHead = nullptr;
 #else // Clang, GCC, and all compatible compilers tend to use __thread.
 static __thread const PrettyStackTraceEntry *PrettyStackTraceHead = nullptr;
 #endif
+#endif
 
+#if ENABLE_BACKTRACE
 static unsigned PrintStack(const PrettyStackTraceEntry *Entry, raw_ostream &OS){
   unsigned NextID = 0;
   if (Entry->getNextEntry())
@@ -107,17 +110,22 @@
   
 #endif
 }
+#endif
 
 PrettyStackTraceEntry::PrettyStackTraceEntry() {
+#if ENABLE_BACKTRACE
   // Link ourselves.
   NextEntry = PrettyStackTraceHead;
   PrettyStackTraceHead = this;
+#endif
 }
 
 PrettyStackTraceEntry::~PrettyStackTraceEntry() {
+#if ENABLE_BACKTRACE
   assert(PrettyStackTraceHead == this &&
          "Pretty stack trace entry destruction is out of order");
   PrettyStackTraceHead = getNextEntry();
+#endif
 }
 
 void PrettyStackTraceString::print(raw_ostream &OS) const {
@@ -132,17 +140,23 @@
   OS << '\n';
 }
 
+#if ENABLE_BACKTRACE
 static bool RegisterCrashPrinter() {
   sys::AddSignalHandler(CrashHandler, nullptr);
   return false;
 }
+#endif
 
 void llvm::EnablePrettyStackTrace() {
+#if ENABLE_BACKTRACE
   // The first time this is called, we register the crash printer.
   static bool HandlerRegistered = RegisterCrashPrinter();
   (void)HandlerRegistered;
+#endif
 }
 
 void LLVMEnablePrettyStackTrace() {
+#if ENABLE_BACKTRACE
   EnablePrettyStackTrace();
+#endif
 }