AddBuildFlags adds the flags common to the build, clean, get, install, list, run, and test commands.

AddModCommonFlags adds the module-related flags common to build commands and 'go mod' subcommands.

BuildInstallFunc is the action for installing a single package or executable.

FindExecCmd derives the value of ExecCmd to use.

ExecCmd is the command to use to run user binaries.

VetExplicit records whether the vet flags were set explicitly on the command line.

VetFlags are the default flags to pass to vet.

VetTool is the path to an alternate vet tool binary.

An Action represents a single action in the action graph.

A Builder holds global state about a build.

BuildMode specifies the build mode: are we just building things or also installing the results?.