Add testing script for iOS x86 build (#26632)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26632

### Summary

This script builds the TestApp (located in ios folder) to generate an iOS x86 executable via the `xcodebuild` toolchain on macOS. The goal is to provide a quick way to test the generated static libraries to see if there are any linking errors. The script can also be used by the iOS CI jobs. To run the script, simply see description below:

```shell
$ruby scripts/xcode_ios_x86_build.rb --help

-i, --install                    path to the cmake install folder
-x, --xcodeproj                  path to the XCode project file
```

### Note

The script mainly deals with the iOS simulator build. For the arm64 build, I haven't found a way to disable the Code Sign using the `xcodebuiild` tool chain (XCode 10). If anyone knows how to do that, please feel free to leave a comment below.

### Test Plan

- The script can build the TestApp and link the generated static libraries successfully
- Don't break any CI job

Test Plan: Imported from OSS

Differential Revision: D17530990

Pulled By: xta0

fbshipit-source-id: f50bef7127ff8c11e884c99889cecff82617212b

ios/TestApp/TestApp/ViewController.mm

@@ -1,5 +1,5 @@
 #import "ViewController.h"
-#import <LibTorch/LibTorch.h>
+#import <torch/script.h>
 
 @interface ViewController ()
 

scripts/xcode_ios_x86_build.rb

@@ -0,0 +1,52 @@
+require 'optparse'
+require 'xcodeproj'
+
+options = {}
+option_parser = OptionParser.new do |opts| 
+ opts.banner = 'Tools for testing the PyTorch iOS x86 build on MacOS'
+ opts.on('-i', '--install ', 'path to the cmake install folder') { |value|
+    options[:install] = value
+ }
+ opts.on('-x', '--xcodeproj ', 'path to the XCode project file') { |value|
+    options[:xcodeproj] = value
+ }
+end.parse!
+puts options.inspect
+
+install_path = File.expand_path(options[:install])
+puts("Library install path: #{install_path}")
+if not Dir.exist? (install_path) 
+    puts "path don't exist:#{install_path}!"
+    exit(false)
+end
+xcodeproj_path = File.expand_path(options[:xcodeproj])
+puts("XCode project file path: #{xcodeproj_path}")
+if not File.exist? (xcodeproj_path) 
+    puts "path don't exist:#{xcodeproj_path}!"
+    exit(false)
+end
+
+project = Xcodeproj::Project.open(xcodeproj_path)
+target = project.targets.first
+header_search_path      = ['$(inherited)', "#{install_path}/include"]
+libraries_search_path   = ['$(inherited)', "#{install_path}/lib"]
+other_linker_flags      = ['$(inherited)', "-all_load"]
+
+target.build_configurations.each do |config|
+    config.build_settings['HEADER_SEARCH_PATHS']    = header_search_path
+    config.build_settings['LIBRARY_SEARCH_PATHS']   = libraries_search_path
+    config.build_settings['OTHER_LINKER_FLAGS']     = other_linker_flags
+end
+
+# link static libraries
+target.frameworks_build_phases.clear
+libs = ['libc10.a', 'libclog.a', 'libeigen_blas.a', 'libcpuinfo.a', 'libpytorch_qnnpack.a', 'libtorch.a']
+for lib in libs do 
+    path = "#{install_path}/lib/#{lib}"
+    libref = project.frameworks_group.new_file(path)
+    target.frameworks_build_phases.add_file_reference(libref)
+end
+project.save
+
+# run xcodebuild
+exec "xcodebuild clean build  -project #{xcodeproj_path}  -target #{target.name} -sdk iphonesimulator -configuration Release"