cmd/link: add script testing facility for linker use
Add support for running script tests as part of the linker's suite of
tests, hooking in the script test engine packages recently moved from
cmd/go to cmd/internal. Linker script tests will use the test binary
itself as the linker for Go builds, and can also run the C compiler if
needed. New script test cases (*.txt files) should be added to the
directory cmd/link/testdata/script.
For demo purposes, this patch also adds a new "randlayout_option.txt"
script test that replicates the existing linker's TestRandLayout
testpoint in script form.
Updates #68606.
Change-Id: Icf26bf657850e39548d6ea819f2542fc68a3899b
Reviewed-on: https://go-review.googlesource.com/c/go/+/601360
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: David Chase <drchase@google.com>