Allocate the basic types inside the LLVMContextImpl instance,

Allocate the basic types inside the LLVMContextImpl instance,
rather than separately with new. Move the members above the
TypeMap members to avoid destruction order issues. This fixes
a leak of these objects, and eliminates an extra level of
indirection in Type::getInt32Ty and friends.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79997 91177308-0d34-0410-b5e6-96231b3b80d8