This CL changes the behavior of 'make install' and 'make test'
in the src/cmd directory and the src/pkg directory to have
each recursive make clean up after itself immediately.

It does the same in test/run, removing $F.$A and $A.out
(the common byproducts) between runs.

On machines with slow disks and aggressive kernel caching,
cleaning up immediately can mean that the intermediate
objects never get written to disk.

This change eliminates almost all the disk waiting during
all.bash on my laptop (a Thinkpad X201s with an SSD running Linux).

147.50u 19.95s 277.34r	before
148.53u 21.64s 179.59r	after

R=golang-dev, r, iant2
CC=golang-dev
https://golang.org/cl/4413042