Disable failing unit tests

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#854

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After #837 merged we see the following three unit tests failing intermittently
only on Windows:

test/CheckedCRewriter/global.c
test/CheckedCRewriter/simple_locals.c
test/CheckedCRewriter/basic_checks.c

In order to unblock our failing ADO builds we are disabling these three tests.
We can enable them when we have these fixed.

See issue checkedc/checkedc-clang#851