Upgrade folly to v2018.10.22.00 for iOS (#21976)

Summary:
Fixes #20302 (For iOS)

Note:
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1. Checked the changes did not break CocoaPods integration.
2. The change for glog copying header into exported/ is to prevent build break for folly.
    `folly/detail/Demangle.h` will try to use libstdc++'s demangle.h. Unfortunately, glog also has a demangle.h in source code. So I copy exported headers and only search headers in exported/ folder during build.
Pull Request resolved: https://github.com/facebook/react-native/pull/21976

Reviewed By: hramos

Differential Revision: D12818131

Pulled By: fkgozali

fbshipit-source-id: b3c637d09d1b3adde0ea15c82eb56e28f846885b