[TargetMachine] Set dso_local if asan is detected

AddressSanitizer instrumentation does not set dso_local on non-thread-local
global variables in -fno-pic and it seems to rely on implied dso_local to work.
Add a hack until we have fixed AddressSanitizer to call setDSOLocal() as
appropriate.

Thanks to Vitaly Buka for reporting the issue and suggesting the way to detect asan.

llvm/lib/Target/TargetMachine.cpp

@@ -163,6 +163,11 @@ bool TargetMachine::shouldAssumeDSOLocal(const Module &M,
     // If the symbol is defined, it cannot be preempted.
     if (!GV->isDeclarationForLinker())
       return true;
+    // FIXME asan does not call setDSOLocal appropriately. Fix asan and delete
+    // the hack.
+    if (RM == Reloc::Static && !GV->isThreadLocal() &&
+        M.getFunction("asan.module_ctor"))
+      return true;
   } else if (TT.isOSBinFormatELF()) {
     // If dso_local allows AsmPrinter::getSymbolPreferLocal to use a local
     // alias, set the flag. We cannot set dso_local for other global values,