If a type doesn't exist in your toolchain, your compile will fail an you will know why.

Conversely, incorrect assumptions about size/size/capacity can lead to subtle run-time bugs.

You have to check sizeof(int) somewhere. Why not do that in a header? To make sure you're using the checked int, define a new type, eg "int4" in that header, too, and use that. Congratulations, you'll fulfill this MISRA rule :)

Or just use int32_t and let the compiler fail if your Toolchain does not have that. Then just write an appropriate header to add it (with the correct checks) ;)