Include -isysroot -arch and -miphoneos-version-min when creating dummy module App.framework

[jmagman]

These extra flags create a framework that can be recognized by CocoaPods, so it knows to embed App.framework later after Flutter creates it.

Add otool test, which is passing: https://ci.chromium.org/p/flutter/builders/try/Mac%20module_test_ios/11940

Fixes flutter/samples#1004

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[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact Hixie on the #hackers channel in Chat (don't just cc him here, he won't see it! He's on Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

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[jmagman]

This test correctly fails on master without the additional flag:

Task result:
{
  "success": false,
  "reason": "Minimum version set to null, expected 9.0"
}

[Hixie]

test-exempt: is a test

[christopherfujino]

LGTM