Adds PrivateDatabase podspec
Adds PrivateDatabase podspec

Summary:
Resolves #16663.

Walked through the reproduction steps in #16663, but with successful build.

We can also now see the files are included in the `Pods` project:

<img width="236" alt="screen shot 2017-11-03 at 7 43 21 pm" src="https://user-images.githubusercontent.com/33126/32390596-4a06c05c-c0cf-11e7-8616-3ae547f8cca2.png">

(I noticed a subspec called `_ignore_me_subspec_for_linting_` so do we have tests for the podspec?)

[IOS] [BUGFIX] [React.podspec] - Resolves build error about missing symbols for PrivateDatabase.{cpp,h}
Closes https://github.com/facebook/react-native/pull/16664

Differential Revision: D6238178

Pulled By: hramos

fbshipit-source-id: b57007ab8c7c8bd0faf1f2f11269a7a2c28183e5

facebook/react-native,exponentjs/react-native,myntra/react-native,facebook/react-native,hoangpham95/react-native,kesha-antonov/react-native,pandiaraj44/react-native,hammerandchisel/react-native,exponent/react-native,facebook/react-native,myntra/react-native,hoastoolshop/react-native,exponent/react-native,Bhullnatik/react-native,pandiaraj44/react-native,jevakallio/react-native,jevakallio/react-native,janicduplessis/react-native,hammerandchisel/react-native,dikaiosune/react-native,kesha-antonov/react-native,javache/react-native,jevakallio/react-native,cdlewis/react-native,ptmt/react-native-macos,ptmt/react-native-macos,janicduplessis/react-native,hoastoolshop/react-native,hoastoolshop/react-native,myntra/react-native,hammerandchisel/react-native,hoangpham95/react-native,javache/react-native,dikaiosune/react-native,myntra/react-native,hammerandchisel/react-native,kesha-antonov/react-native,hoangpham95/react-native,javache/react-native,rickbeerendonk/react-native,kesha-antonov/react-native,javache/react-native,cdlewis/react-native,Bhullnatik/react-native,hammerandchisel/react-native,myntra/react-native,rickbeerendonk/react-native,cdlewis/react-native,jevakallio/react-native,arthuralee/react-native,Bhullnatik/react-native,hoangpham95/react-native,hammerandchisel/react-native,kesha-antonov/react-native,exponentjs/react-native,jevakallio/react-native,javache/react-native,janicduplessis/react-native,exponentjs/react-native,rickbeerendonk/react-native,pandiaraj44/react-native,rickbeerendonk/react-native,Bhullnatik/react-native,ptmt/react-native-macos,rickbeerendonk/react-native,exponent/react-native,hoangpham95/react-native,facebook/react-native,Bhullnatik/react-native,facebook/react-native,myntra/react-native,hoastoolshop/react-native,cdlewis/react-native,exponent/react-native,arthuralee/react-native,cdlewis/react-native,jevakallio/react-native,arthuralee/react-native,hoangpham95/react-native,hammerandchisel/react-native,dikaiosune/react-native,hoastoolshop/react-native,arthuralee/react-native,hoastoolshop/react-native,exponentjs/react-native,rickbeerendonk/react-native,ptmt/react-native-macos,janicduplessis/react-native,facebook/react-native,exponent/react-native,jevakallio/react-native,hoastoolshop/react-native,hoastoolshop/react-native,janicduplessis/react-native,myntra/react-native,exponentjs/react-native,jevakallio/react-native,janicduplessis/react-native,pandiaraj44/react-native,rickbeerendonk/react-native,ptmt/react-native-macos,exponent/react-native,kesha-antonov/react-native,jevakallio/react-native,janicduplessis/react-native,ptmt/react-native-macos,javache/react-native,dikaiosune/react-native,ptmt/react-native-macos,cdlewis/react-native,myntra/react-native,Bhullnatik/react-native,rickbeerendonk/react-native,pandiaraj44/react-native,pandiaraj44/react-native,facebook/react-native,cdlewis/react-native,arthuralee/react-native,cdlewis/react-native,exponentjs/react-native,kesha-antonov/react-native,dikaiosune/react-native,exponentjs/react-native,Bhullnatik/react-native,exponent/react-native,cdlewis/react-native,exponentjs/react-native,myntra/react-native,kesha-antonov/react-native,ptmt/react-native-macos,facebook/react-native,javache/react-native,pandiaraj44/react-native,kesha-antonov/react-native,pandiaraj44/react-native,dikaiosune/react-native,javache/react-native,dikaiosune/react-native,hoangpham95/react-native,Bhullnatik/react-native,hoangpham95/react-native,facebook/react-native,javache/react-native,rickbeerendonk/react-native,hammerandchisel/react-native,dikaiosune/react-native,exponent/react-native,janicduplessis/react-native