Disable bitcode for iOS CI jobs (#26478)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26478
### Summary
Since QNNPACK [doesn't support bitcode](https://github.com/pytorch/QNNPACK/blob/7d2a4e9931a82adc3814275b6219a03e24e36b4c/scripts/build-ios-arm64.sh#L40), I'm going to disable it in our CMake scripts. This won't hurt any existing functionalities, and will only affect the build size. Any application that wants to integrate our framework should turn off bitcode as well.
### Test plan
- CI job works
- LibTorch.a can be compiled and run on iOS devices
Test Plan: Imported from OSS
Differential Revision: D17489020
Pulled By: xta0
fbshipit-source-id: 950619b9317036cad0505d8a531fb8f5331dc81f
