internal/imports: add buildflags to ProcessEnv

This change adds a buildflags variable to the ProcessEnv inside internal/imports. When you run go list with GO111MODULE=on to get information about the package you are in, it will add a go directive to your go.mod file if there is not one. With the tempModfile=on flag, there should be no changes to a user's go.mod file.

Updates golang/go#36247

Change-Id: I817e4c46b4f433d0665fcb7585fcdf4f87049a38
Reviewed-on: https://go-review.googlesource.com/c/tools/+/215978
Run-TryBot: Rohan Challa <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>

Author: ridersofrohan

internal/lsp/cache/view.go

@@ -373,6 +373,12 @@ func (v *view) buildProcessEnv(ctx context.Context) (*imports.ProcessEnv, error)
 			env.GOSUMDB = split[1]
 		}
 	}
+	if len(cfg.BuildFlags) > 0 {
+		if env.GOFLAGS != "" {
+			env.GOFLAGS += " "
+		}
+		env.GOFLAGS += strings.Join(cfg.BuildFlags, " ")
+	}
 	return env, nil
 }