Modify the code that emits the module flags to use the new module flags accessor

Modify the code that emits the module flags to use the new module flags accessor
method. This allows the target lowering code to not have to deal with MDNodes.

Also, avoid leaking memory like a sieve by not creating a global variable for
the image info section, but just emitting the code directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@150624 91177308-0d34-0410-b5e6-96231b3b80d8