Add a BUGS section and copy the wording from mmap(2)'s MAP_NOSYNC, documenting the obsoleteness of the msync(2) syscall and its single remaining purpose.
Add a BUGS section and copy the wording from mmap(2)'s MAP_NOSYNC,
documenting the obsoleteness of the msync(2) syscall and its single
remaining purpose.

PR:		70916
Submitted by:	Radim Kolar <hsn@netmag.cz>
MFC after:	3 days

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