The test.bash file generates .so file using gcc, builds the executable
using the go tool and then run it with the $LD_LIBRARY_PATH variable
pointing to the directory where the .so file lives.
Fixes#2982.
R=rsc, remyoudompheng
CC=golang-dev
https://golang.org/cl/5788043
Does not actually test so files.
««« original CL description
misc/cgo: re-enable testso
Also enabled it for darwin.
R=rsc
CC=golang-dev
https://golang.org/cl/5754063
»»»
R=golang-dev, minux.ma, r, f
CC=golang-dev
https://golang.org/cl/5756075