misc/cgo: re-enable testso

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
7 files changed