Use address-taken to disambiguate global variable and indirect memops.

Major steps include:
 1). introduces a not-addr-taken bit-field in GlobalVariable
 2). GlobalOpt pass sets "not-address-taken" if it proves a global varirable 
    dosen't have its address taken.
 3). AA use this info for disambiguation. 


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193251 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AsmParser/LLLexer.cpp

@@ -504,6 +504,7 @@ lltok::Kind LLLexer::LexIdentifier() {
   KEYWORD(zeroinitializer);
   KEYWORD(undef);
   KEYWORD(null);
+  KEYWORD(notaddrtaken);
   KEYWORD(to);
   KEYWORD(tail);
   KEYWORD(target);