run.bash: skip -static cgo test if -static linking isn't possible. Some system doesn't have libc.a available.
run.bash: skip -static cgo test if -static linking isn't possible.
Some system doesn't have libc.a available.

While we're at here, also export GOROOT in run.bash, so that
one doesn't need to set GOROOT to run run.bash.

LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/99870043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang