MFC r256815:

  Calculate the baud rate divisor rather than using a hard-coded value.
MFC	r258115 (partial);

gperf: bring a small update from Apple Developers tools 4.4

From [1]

offset.patch
Makes use the C offsetof() macro.

We are not merging the size_type.patch as it raises some
(apparently) bogus warnings and is not really used.

[1] http://opensource.apple.com/source/gperf/gperf-9/patches/