Conflict between glibc and Mach headers

[Igor Khavkine]

Glibc has a header which goes into /usr/include/mach_init.h
and Mach has a header which goes into /usr/include/mach/vm_param.h.

Both of them define the macros `round_page' and `trunc_page'. The
former in terms of the variable `__vm_page_size' and the latter
in terms of the constant macro `PAGE_SIZE'.

Was it intended for these headers not to be used together?
And why is there a variable for the page size, is it not a
constant which can be known at compile time?

Thanks.

Igor