[exceptions] Upgrade exception handlers when stack protector is used

Summary:
MSVC provide exception handlers with enhanced information to deal with security buffer feature (/GS).

To be more secure, the security cookies (GS and SEH) are validated when unwinding the stack.

The following code:
```
void f() {}

void foo() {
  __try {
    f();
  } __except(1) {
    f();
  }
}
```

Reviewers: majnemer, rnk

Subscribers: thakis, llvm-commits, chrisha

Differential Revision: http://reviews.llvm.org/D21101

llvm-svn: 274239

0 files changed, 0 insertions, 0 deletions