Missing checks in calls to variadic functions inside checked scope

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#1177

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checkedc/checkedc-clang#1174 added support to call variadic functions in checked scope. There are several checks which are yet to be implemented. The PR does not do any bounds checking for the arguments to printf/scanf like functions. The following issues were raised by @mattmccutchen-cci on the PR.

[secure-sw-dev-bot]

Comment from @mgrang:

Duplicate of checkedc/checkedc-clang#1178