ProcessDashC gets the command line arguments passed to a "go" command (without "go" itself), and processes the "-C" flag present at the beginning of the slice (if present), changing directories as requested, then returns the slice without it.

Run takes a go command ("build", "install", etc...) with its arguments, and applies changes specified through opts to the command before running it in a different process.

WithToolexec forces a call to Run() to build with the -toolexec option when wrapping a build command.