Fix glog command line arguments on a clean build

[jeroen-dhollander]

To support glog's command line arguments like --logtostderr, it requires gflags.

If gflags is not found, glog will still compile but the command line arguments will be absent.

As glog was created before gflags, that was the case on a clean build.
Note that on subsequent builds gflags already existed, so a second build 'magically' made the command line arguments appear.

Pull Request Template

Title: glog flags like --logtostderr are missing on a clean build

Description:

See facebook/openr#28

Test Plan:

• On my OpenR code I compiled it before and after the reorder, and noticed the different behavior.
• No additional testing was performed for this fbzmq fix.

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[facebook-github-bot]

@saifhhasan is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.