[TLI] Support for per-Function TLI that overrides available libfuncs

Summary:

Follow-on to D66428 and D71193, to build the TLI per-function so
that -fno-builtin* handling can be migrated to use function attributes.
See discussion on D61634 for background. This is an enabler for fixing
handling of these options for LTO, for example.

With D71193, the -fno-builtin* flags are converted to function
attributes, so we can now set this information per-function on the TLI.

In this patch, the TLI constructor is changed to take a Function, which
can be used to override the available builtins. The TLI is augmented
with an array that can be used to specify which builtins are not
available for the corresponding function. The available function checks
are changed to consult this override before checking the underlying
module level baseline TLII. New code is added to set this override
array based on the attributes.

I also removed the code that sets availability in the TLII in clang from
the options, which is no longe...