Supported Platforms
Firstly, some assumptions about the platforms the language targets, just to get a few things out of the way. An implementation will not be able to support all the language features if some of these assumptions are not met.
Note that these do not imply hardware support, merely compiler support; the difference is most relevant for floating-point and 64-bit integer types.
<stdint.h> is available or can be implemented, with [u]int{8,16,32,64}_t and [u]intptr_t types present.