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The C Standard further explains in a footnote,
The intent is that an implementation should identify the nature of, and where possible localize, each violation. Of course, an implementation is free to produce any number of diagnostics as long as a valid program is still correctly translated. It may also successfully translate an invalid program.
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The motivation behind this constraint lies in the semantics of inline definitions. Paragraph 7 of subclause 6.7.4 reads, in part:
An inline definition provides an alternative to an external definition, which a translator may use to implement any call to the function in the same translation unit. It is unspecified whether a call to the function uses the inline definition or the external definition.
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