all: REVERSE MERGE dev.cmdgo (60c7cb1) into master

This commit is a REVERSE MERGE.
It merges dev.cmdgo back into its parent branch, master.
This marks the end of development on dev.cmdgo.

Merge List:

+ 2021-08-27 60c7cb1d96 [dev.cmdgo] all: merge master (cc0c8c9) into dev.cmdgo
+ 2021-08-26 74e26def12 [dev.cmdgo] all: merge master (ec59abc) into dev.cmdgo
+ 2021-08-25 872da90a12 [dev.cmdgo] cmd/go: fix calls to modFileGoVersion to pass in modFile
+ 2021-08-25 1a46b9229e [dev.cmdgo] cmd/go: clean up TODOWorkspaces instances
+ 2021-08-25 04573ac [dev.cmdgo] all: merge master (543de0a) into dev.cmdgo
+ 2021-08-12 d1bce0062a [dev.cmdgo] cmd/link: fix TestBuildForTvOS
+ 2021-08-12 9246175d3d [dev.cmdgo] don't give command-line-arguments a module
+ 2021-08-11 71a5f6373a [dev.cmdgo] cmd/go: remove modload.ModRoot function
+ 2021-08-06 73a27d189c [dev.cmdgo] cmd/go: address code review comments in test cgo_path_space_quote
+ 2021-08-06 df087a501c [dev.cmdgo] cmd: update x/tools and remove copy of txtar
+ 2021-07-31 8efed76ac0 [dev.cmdgo] cmd/go: add go mod editwork command
+ 2021-07-30 79de9e0b10 [dev.cmdgo] cmd/go: thread through modroots providing replacements
+ 2021-07-30 cd2d68df96 [dev.cmdgo] cmd/go: provide a more helpful missing required module error in workspaces
+ 2021-07-30 6f40441dd8 [dev.cmdgo] cmd/go: allow expliticly setting -mod=readonly in workspace mode
+ 2021-07-30 e5a7027c0c Merge "[dev.cmdgo] all: merge master (19f3f56) into dev.cmdgo" into dev.cmdgo
+ 2021-07-30 d4f57afe2a [dev.cmdgo] cmd: support space and quotes in CC and CXX
+ 2021-07-30 9bcab3cd64 [dev.cmdgo] cmd/internal/str: add utilities for quoting and splitting args
+ 2021-07-30 2890426232 [dev.cmdgo] cmd/internal/str: move package from cmd/go/internal/str
+ 2021-07-28 45790ed3b7 [dev.cmdgo] all: merge master (19f3f56) into dev.cmdgo
+ 2021-07-28 163f210115 [dev.cmdgo] cmd/go: sort roots when joining multiple main module roots
+ 2021-07-28 70e7b03e17 [dev.cmdgo] cmd/go: maintain a go.work.sum file
+ 2021-07-27 9006e438c5 [dev.cmdgo] cmd/go: make fewer 'go mod' commands update go.mod
+ 2021-07-27 a071c1af8a [dev.cmdgo] cmd/go: add -testsum flag to update go.sum in script tests
+ 2021-07-27 211f2f5076 [dev.cmdgo] cmd/go: add go mod initwork command
+ 2021-07-27 a6b4830139 [dev.cmdgo] cmd/go: fold index and modFile into MainModules
+ 2021-07-26 25e992b183 [dev.cmdgo] cmd/go: add the workspace mode
+ 2021-07-26 1b066c5de0 [dev.cmdgo] cmd: pull in x/mod on the dev.cmdgo branch
+ 2021-07-22 e660828ae3 [dev.cmdgo] cmd/go: replace Target with MainModules, allowing for multiple targets
+ 2021-07-20 cbb8a75986 [dev.cmdgo] cmd/go/testdata/script: fix a small typo in modfile_flag
+ 2021-07-06 53c56b0 [dev.cmdgo] all: merge master (cc03398) into dev.cmdgo
+ 2020-12-22 6dc2c16f95 [dev.cmdgo] codereview.cfg: add config for dev.cmdgo

Change-Id: Ic42f1273e42c90954bd61a6e4d6ca193c97bf04c