[clang] Remove a FIXME that we can't fix

[thakis]

Summary

I added this recently, but it looks like several tests very intentionally
check that -mios-version-min=foo --target=x86_64-apple-ios does simulator
builds. So we can't easily remove this hack, even though it makes little
sense in an arm mac world. (Here, you _have_ to say
-mios-simulator-version-min= or --target=arm64-apple-ios-simulator.)

The tests that check this:

Clang :: Driver/darwin-ld.c
Clang :: Driver/darwin-simulator-macro.c
Clang :: Driver/darwin-version.c

No behavior change.

[hans]

lgtm

"No behavior change." occurs twice in the change description.

[thakis]

Thanks, fixed commit message.

clang/lib/Driver/ToolChains/Darwin.cpp

if (!Driver::GetReleaseVersion(OSTarget->getOSVersion(), Major, Minor,
         HadExtra || Major < 19 || Major >= 100 || Minor >= 100 || Micro >= 100)
       getDriver().Diag(diag::err_drv_invalid_version_number)
           << OSTarget->getAsString(Args, Opts);
   } else
     llvm_unreachable("unknown kind of Darwin platform");
 
   DarwinEnvironmentKind Environment = OSTarget->getEnvironment();
   // Recognize iOS targets with an x86 architecture as the iOS simulator.
-  // FIXME: Remove this.
   if (Environment == NativeEnvironment && Platform != MacOS &&
       Platform != DriverKit && OSTarget->canInferSimulatorFromArch() &&
       getTriple().isX86())
     Environment = Simulator;
 
   VersionTuple NativeTargetVersion;
   if (Environment == MacCatalyst)
     NativeTargetVersion = OSTarget->getNativeTargetVersion();