Fix typo in llvm/lib/Target/README.txt

[siddhesh]

Summary

Trivial typo, replace __builtin_objectsize with __builtin_object_size.

[siddhesh]

I do not have commit access, so please commit the change for me. Thanks!

llvm/lib/Target/README.txt

 
 This occurs several times in viterbi.
 
 Note that this would change the semantics of @llvm.objectsize which by its
 current definition always folds to a constant. We also should make sure that
 we remove checking in code like
 
   char *p = malloc(strlen(s)+1);
-  __strcpy_chk(p, s, __builtin_objectsize(p, 0));
+  __strcpy_chk(p, s, __builtin_object_size(p, 0));
 
 //===---------------------------------------------------------------------===//
 
 clang -O3 currently compiles this code
 
 int g(unsigned int a) {
   unsigned int c[100];
   c[10] = a;