Don’t allow the compiler to convert malloc + memset into calloc,
causing a recursive call in _calloc_r. Fixes crash when building with
-O2 optimization level.
* Philosophical: "explicit is better than implicit".
* Practical: Allows useful errors if invalid directories given in components as the defaults aren't
always used. Also trims the -I path from a number of components that have no actual include
directory.
* Simplifies knowing which components will be header-only and which won't
