Be more restrictive about max frame size.

exec and realpath both have PATH_MAX buffers (which is a bug in its own
right, since PATH_MAX isn't a real limit). The printf/scanf implementation
has a few large functions, and the DNS implementation is a complete 1970s
C nightmare.

Bug: http://b/30032507
Change-Id: I4b9daa552123c16bbe84f0632b2b32eba17a9dbd