The static func named thread in issue5337.go's C snippet
conflicts with the static func named thread in issue3350.go's C snippet.
I don't know why (they're both static) but I also don't care,
because -linkmode=internal only needs to be able to handle
the cgo in the standard library, and it does.

Change the test to avoid this problem.

Fixes build (after run.bash is fixed to detect the breakage).

R=minux.ma
TBR=minux.ma
CC=golang-dev
https://golang.org/cl/11201043