Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_mac.cc
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_mac.cc
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_mac.cc
@@ -564,10 +564,14 @@
   return false;
 }
 
-extern "C" double dyldVersionNumber;
+extern "C" SANITIZER_WEAK_ATTRIBUTE double dyldVersionNumber;
 static const double kMinDyldVersionWithAutoInterposition = 360.0;
 
 bool DyldNeedsEnvVariable() {
+  // Although sanitizer support was added to LLVM on OS X 10.7+, GCC users
+  // still may want use them on older systems. On older Darwin platforms, dyld
+  // doesn't export dyldVersionNumber symbol and we simply return true.
+  if (!&dyldVersionNumber) return true;
   // If running on OS X 10.11+ or iOS 9.0+, dyld will interpose even if
   // DYLD_INSERT_LIBRARIES is not set. However, checking OS version via
   // GetMacosVersion() doesn't work for the simulator. Let's instead check