Make TypeBuilder's result depend on the LLVMContext it's passed.

Make TypeBuilder's result depend on the LLVMContext it's passed.
TypeBuilder was using a local static variable to cache its result. This made it
ignore changes in its LLVMContext argument and always return a type constructed
from the argument to the first call.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81316 91177308-0d34-0410-b5e6-96231b3b80d8