Which supported platform does not support native booleans?

internal.h defines GLFWbool as an int and glfw3.h defines GLFW_TRUE as 1 and GLFW_FALSE as 0. This indicates that there is no boolean type available on some supported platform/standard library/etc. . Is this still the case and if so, which platform would that be?

Afaik it is more because of language than platform. C89 does not have bool type.