[libc] move sys/mman macros to /include

Previously the mman macros were in api.td, but platform differences are
easier to handle with preprocessor macros so they have been moved to
include. Also I completed the list of macros (at least for what I need
soon) and fixed some previously incorrect values.

Reviewed By: sivachandra, lntue

Differential Revision: https://reviews.llvm.org/D134491