stand: Add macros for file types from stat

Add the familiar macros for file types for stat's st_mode
member. Prepend HOST_ to the start of these. Make sure all the values
match the linux nolibc and uapi headers. These values are the same as
native values since they appear to be required by POSIX. Define anyway
to allow the reader of the code to know that they are in the 'host (eg
Linux)' namespace rather than the 'loader' namespace.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D37967