The "elf.h" header changes involve only comments, the released
Plan 9 C preprocessing function does not cope with multiline
comments following the #define keyword.  All multiline comments
have been moved to the line above the associated definition.
Sigh!  Fixing the Plan 9 compiler is not an option.

<time.h> does not exist in the Plan 9 Native library.  I have
moved it from src/cmd/ld/pe.h to include/u.h. RSC correctly points
out that this copy of <u.h> is not the one used to compile the
Go release on Plan 9 platforms.

R=golang-dev
CC=golang-dev, rsc
https://golang.org/cl/4574042