Guards for older GCC versions

[teeks99]

Fixes #4156

[grpc-kokoro]

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[grpc-kokoro]

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[teeks99]

I signed it!

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We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.
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[teeks99]

I added my e-mail.

[googlebot]

CLAs look good, thanks!

[xfxyjwf]

@teeks99 Thanks for the patch. Though I don't think we want to support gcc version < 4.6 any more. Right now our master branch requires at least g++ 4.8 to build.