In addition to adding the library, change the way the anames array is created.
Previously, it was written to src/cmd/6l/enam.c (and similarly for 5l and 8l)
and each of the other tools (6g, 6c, 6a) compiled the 6l/enam.c file in addition
to their own sources.

Now that there is a library shared by all these programs, move the anames
array into that library. To eliminate name conflicts, name the array after
the architecture letter: anames5, anames6, anames8.

First step to linker cleanup (golang.org/s/go13linker).

This CL does not build by itself. It depends on the CLs introducing
liblink and changing commands to use it.

R=iant
CC=golang-dev
https://golang.org/cl/35740044