cmd/go: in TestScript/mod_outside, run 'go build' before checking cmd/addr2line staleness

If the build cache is cleaned (using 'go clean -cache' or similar), or
if a toolchain is freshly installed without warming the cache, the
build cache might not contain the dependencies needed to verify that
cmd/addr2line is not stale. In that case, the test should refill the
cache instead of failing.

Fixes #56889.

Change-Id: Ic6cf13b92bafa9c795e50eb0e4e1a9ae00ee8538
Reviewed-on: https://go-review.googlesource.com/c/go/+/452458
Auto-Submit: Bryan Mills <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Russ Cox <[email protected]>

Author: Bryan C. Mills

src/cmd/go/testdata/script/mod_outside.txt

@@ -205,6 +205,7 @@ stderr 'needmod[/\\]needmod.go:10:2: no required module provides package example
 
 # 'go install' for a package in GOROOT should succeed.
 # (It must be non-stale here so that the test does not write to GOROOT).
+go build -o $devnull cmd/addr2line  # make sure any necessary dependencies are present in GOCACHE
 ! stale cmd/addr2line
 go install cmd/addr2line
 ! stderr .