And it doesn't for the compiler in question either. As long as the headers exist in the places it looks for them. No compiler magically knows where the headers are if you haven't placed them in the right location
replystddef.h (et al) should be shipped by the compiler itself, and so it should know where it is. But they rely on gcc for it, hence it doesn't always know where to look. Seems totally fine for a prototype.
replyEspecially given they're not shipping anything. The GCC binaries can't find misplaced or not installed headers either.
replyWould you accept the same quality of implementation from a human team?
replyA compiler that can't magically know how to find headers that don't exist in the expected directory?
replyYes, that is the case for pretty much every compiler. I suppose you could build the headers into the binary, but nobody does that.