MS Compat: mark globals emitted in read-only sections const

They cannot be written to, so marking them const makes sense and may improve
optimisation.

As a side-effect, SectionInfos has to be moved from Sema to ASTContext.

It also fixes this problem, that occurs when compiling ATL:

  warning LNK4254: section 'ATL' (C0000040) merged into '.rdata' (40000040) with different attributes

The ATL headers are putting variables in a special section that's marked
read-only. However, Clang currently can't model that read-onlyness in the IR.
But, by making the variables const, the section does become read-only, and
the linker warning is avoided.

Differential Revision: http://reviews.llvm.org/D5812

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219960 91177308-0d34-0410-b5e6-96231b3b80d8
Insert poisoned paddings between fields in C++ classes so that AddressSanitizer can find intra-object-overflow bugs

Summary:
The general approach is to add extra paddings after every field
in AST/RecordLayoutBuilder.cpp, then add code to CTORs/DTORs that poisons the paddings
(CodeGen/CGClass.cpp).

Everything is done under the flag -fsanitize-address-field-padding. 
The blacklist file (-fsanitize-blacklist) allows to avoid the transformation 
for given classes or source files. 

See also https://code.google.com/p/address-sanitizer/wiki/IntraObjectOverflow

Test Plan: run SPEC2006 and some of the Chromium tests with  -fsanitize-address-field-padding

Reviewers: samsonov, rnk, rsmith

Reviewed By: rsmith

Subscribers: majnemer, cfe-commits

Differential Revision: http://reviews.llvm.org/D5687

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219961 91177308-0d34-0410-b5e6-96231b3b80d8
trying to fix the new test on hexagon-build

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219965 91177308-0d34-0410-b5e6-96231b3b80d8
test/CodeGen/sections.c: add triple

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@219969 91177308-0d34-0410-b5e6-96231b3b80d8