cmd/compile: evaluate the need for shortcircuit

[brtzsnr]

For Go1.8

1. What version of Go are you using (go version)?
   go version devel +097e2c0 Mon May 2 21:02:54 2016 +0000 linux/amd64
2. What operating system and processor architecture are you using (go env)?
   linux/amd64
3. What did you do?
   ./make.bash & check the size of binaries in pkg/tools/linux_amd64
4. What did you expect to see?
5. What did you see instead?

Shortcircuit pass increases the size of the binary by approx 0.04%, but this is not consistent.

with shortcircuit
3244469 addr2line
4909014 api
3982946 asm
3988940 cgo
10647306 compile
4914435 cover
3424419 dist
3825731 doc
2916445 fix
4070497 link
3207010 nm
3532598 objdump
1996235 pack
9308102 pprof
8435425 trace
6246651 vet
2879901 yacc
81530124 total

without shortcircuit
3236277 addr2line
4904918 api
3978850 asm
3993036 cgo // higher
1063898 compile
4906243 cover
3424419 dist
3825731 doc
2916445 fix
4070497 link
3207010 nm
3536694 objdump // higher
1996235 pack
9304006 pprof
8435425 trace
6242555 vet
2875805 yacc
81493134 total

[randall77]

I originally added shortcircuit to fix some bad generation of && and ||. If we're able to generate reasonable code for those ops without using shortcircuit, then we should get rid of it.