Test codegen when setting deployment target

[madsmtm]

Test our codegen in different scenarios when setting the deployment target. There are many places here where this is still incorrect, these will be fixed in #129342, #129367 and #129369. See #129432 for the bigger picture.

Tested locally using:

./x test tests/run-make/apple-deployment-target --target="aarch64-apple-darwin,aarch64-apple-ios,aarch64-apple-ios-macabi,aarch64-apple-ios-sim,aarch64-apple-tvos,aarch64-apple-tvos-sim,aarch64-apple-visionos,aarch64-apple-visionos-sim,aarch64-apple-watchos,aarch64-apple-watchos-sim,arm64_32-apple-watchos,armv7s-apple-ios,i386-apple-ios,x86_64-apple-darwin,x86_64-apple-ios,x86_64-apple-ios-macabi,x86_64-apple-tvos,x86_64-apple-watchos-sim,x86_64h-apple-darwin"

The only Apple targets that aren't tested by the above command are:

• arm64e-apple-darwin, failed to build, see Support arm64e-apple-darwin cc-rs#1205.
• armv7k-apple-watchos, failed to link, see armv7k-apple-watchos fails to link #130071.
• arm64e-apple-ios, failed to link, see Apple arm64e targets fail to link with newer Xcode 15 #130085.
• i686-apple-darwin, requires a bit of setup and an older machine, see the docs.
• i386-apple-ios requires you to set IPHONEOS_DEPLOYMENT_TARGET=10.0 for the test helpers to work, will be fixed by Don't specify -arch and -m{}os-version-min= on Apple platforms cc-rs#1030.

But all of this is as it was before this PR.

Fixes #47825, since we now have a test that compiles a dylib for aarch64-apple-ios.

Split out from #129342, see that for a little bit of the review that this has gone through already.

r? petrochenkov

@rustbot label O-apple