[llvm] [libc][bazel] add rules to build the scanf family (PR #128082)

[Aaron Siddhartha Mondal via llvm-commits]

https://github.com/aaronmondal approved this pull request.

You might want to use the term `targets` instead of `rules` in the PR title. A `rule` would be something like the implementation of the `binary_alias`: https://github.com/llvm/llvm-project/blob/5e26fb169936ca1e24da6698ce895fec99af06c2/utils/bazel/llvm-project-overlay/llvm/binary_alias.bzl#L25

The `libc_support_library` is in fact not a rule but a `macro`. You can see this because there is no `rule` keyword anywhere in its definition and instead it's effectively just a regular function defined via `def`: https://github.com/llvm/llvm-project/blob/5e26fb169936ca1e24da6698ce895fec99af06c2/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl#L70

Ultimately this macro expands to `targets`, i.e. instantiations of the `cc_library` rule:


https://github.com/llvm/llvm-project/blob/5e26fb169936ca1e24da6698ce895fec99af06c2/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl#L58

https://github.com/llvm/llvm-project/pull/128082