[UpdateCCTestChecks] Include generated functions if asked

Add the --include-generated-funcs option to update_cc_test_checks.py so that any
functions created by the compiler that don't exist in the source will also be
checked.

We need to maintain the output order of generated function checks so that
CHECK-LABEL works properly.  To do so, maintain a list of functions output for
each prefix in the order they are output.  Use this list to output checks for
generated functions in the proper order.

Differential Revision: https://reviews.llvm.org/D83004