In new API, let's avoid types whose size/layout depends on the C compiler.

• Bad: long, bitfields, enums
• OK:
  • size_t, intptr_t, which depend directly on the platform
  • int for small ranges (as replacement for enum) -- here practicality beats purity
• Good: int32_t etc.

In the existing API, we might maybe want to e.g. replace long by int32_t, and declare an ABI break on the few platforms where sizeof(long) != sizeof(int32_t).