kGlibcxxVer, from _GLIBCXX_RELEASE
kGlibcxxVer, from _GLIBCXX_RELEASE

Summary: [Folly] `kGlibcxxVer`, from `_GLIBCXX_RELEASE` if available.

Differential Revision: D15209042

fbshipit-source-id: 077e94db623f33ebc3ec2cb93a5d7774d384a863

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly