C99 #define macros don't show up in Apiview

See https://apiview.dev/Assemblies/Review/2339253c7f1343dabf7d78ee5b4496aa#az_span.h

We don't see some of the #define macros:
https://github.com/Azure/azure-sdk-for-c/blob/c12a0107925b004be6f130f986999b33acd1c9fa/sdk/inc/azure/core/az_span.h#L78-L111
cc @pakrym, @RickWinter

Inspect the Apiview review at the linked apiview.dev URL and compare it with the C99 macro definitions in sdk/inc/azure/core/az_span.h, lines 78-111, at the referenced commit. Trace how those definitions are processed and verify that the missing #define macros appear in the resulting Apiview output.

Written by the indexing model from the issue text.