MFC r226422, r227241, r228063, r228697, r228698, r228701, r234310, r234850,
r250226, r250926.

This brings m4 up to date with the version in head and fixes the eval
command when called with a 2nd and 3rd argument.  The only differences
remaining are related to the updated flex and byacc in head.

PR:		bin/166994