A temporary fix based on discussions in #128079
Currently, baremetal targets are failing to build because the scanf
internals require FILE* (either from the system's libc or our libc).
Normally we'd just turn off the broken entrypoint, but since the scanf
internals are built separately that doesn't work. This patch adds extra
conditions to building those internals, which we can hopefully remove
once we have a proper way to build scanf for embedded.
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