cmd/go: use the resolved buildmode in build IDs and build info

When -buildmode=default is used, the link action ID hashed the
literal string "default", so building with -buildmode=default and
building with the buildmode it resolves to produced binaries that
were identical except for their build IDs. Hash the resolved
buildmode (ldBuildmode) instead, so that equivalent builds share a
build ID and cached link outputs.

Additionally, the build info stamped into binaries normalized
-buildmode=default to "exe" without accounting for platforms where
the default is PIE (android, ios, darwin, and windows without
-race), misreporting the buildmode actually given to the linker.
Record "pie" on those platforms instead.

Together these make it possible to reproduce a binary built with
-buildmode=default from its stamped build info alone.

Fixes #63559

Change-Id: If3ac6a6a84fbf20097ff3009e228ce07705d6835
GitHub-Last-Rev: 1ddf5bfef00c64cc589d90e4e8bf4257f8d05b88
GitHub-Pull-Request: golang/go#80312
Reviewed-on: https://go-review.googlesource.com/c/go/+/798680
Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Sean Liao <sean@liao.dev>
Reviewed-by: Michael Pratt <mpratt@google.com>
6 files changed
tree: 34866a49804fa56d1e9420e27754f56b40275a75
  1. .github/
  2. api/
  3. doc/
  4. lib/
  5. misc/
  6. src/
  7. test/
  8. .gitattributes
  9. .gitignore
  10. codereview.cfg
  11. CONTRIBUTING.md
  12. go.env
  13. LICENSE
  14. PATENTS
  15. README.md
  16. SECURITY.md
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