Why are __int8 and friends macros?

When ms-extensions are turned on, __int8 becomes a #define for char.
Likewise for __int16, __int32 and __int64 ... all #defines. This is not
compatible with the MS compiler, where these are all actual keywords. A
program can detect the difference by simply doing:

  #ifdef __int8
  #error __int8 should not be a macro
  #endif

I'd like to fix this, but I thought I'd ask first since it seems to have
been done this way intentionally (although I can't imagine why).

I don't think it is intentional.. Feel free to fix it.. that's
something I need also since it creates a slight incompatibility
between clang -E and cl -E.