Unlike LLVM, Subzero does not store the type of value a pointer
references as part of the pointer's type information. So add a type
argument to createGEP(). Also add the type to createStore(), to
enable smaller types to be emulated by larger ones.

Bug swiftshader:11

Change-Id: I08173dd0ba07362d2b27baff4a8fba0ecce093d2
Reviewed-on: https://swiftshader-review.googlesource.com/7392Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>