Add experimental clang/driver flag -fsanitize-address-field-padding=N

Summary:
This change adds an experimental flag -fsanitize-address-field-padding=N (0, 1, 2)
to clang and driver. With this flag ASAN will be able to detect some cases of
intra-object-overflow bugs,
see https://code.google.com/p/address-sanitizer/wiki/IntraObjectOverflow

There is no actual functionality here yet, just the flag parsing.
The functionality is being reviewed at http://reviews.llvm.org/D5687

Test Plan: Build and run SPEC, LLVM Bootstrap, Chrome with this flag.

Reviewers: samsonov

Reviewed By: samsonov

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5676

llvm-svn: 219417

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1628,6 +1628,9 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
       break;
     }
   }
+  // -fsanitize-address-field-padding=N has to be a LangOpt, parse it here.
+  Opts.Sanitize.SanitizeAddressFieldPadding =
+      getLastArgIntValue(Args, OPT_fsanitize_address_field_padding, 0, Diags);
 }
 
 static void ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,