Add the Flags field to the Config struct in packages to provide a way
for users to pass along additional information to the underlying query
tool.
Since users that need Flags will already know something about the build
system they are using (and flags will vary depending on the underlying
build system), they can pass through the flags that they need for that
build system.
For example, build tags should be passed through using the Flags field in go build,
using "-tags=".
Change-Id: Ia65bf0d003db2f6d9aaad6cd09c602f4bc5bf3e3
Reviewed-on: https://go-review.googlesource.com/125302
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
8cc4e8a6f4