Fixes building for Apple TVOS platform.

prior to this, we get incorrect sysroot and arch target. Snippet of the build Log is below

```
/Applications/Xcode10.2.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS12.2.sdk -miphoneos-version-min=5.0 -fPIC -dynamiclib -miphoneos-version-min=5.0   -o 2048_libretro_ios.dylib ./libretro.o ./game_noncairo.o ./game_shared.o  -lm
15:11:47 clang: warning: using sysroot for 'AppleTVOS' but targeting 'iPhone' [-Wincompatible-sysroot]
15:11:47 ld: warning: ignoring file /Applications/Xcode10.2.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS12.2.sdk/usr/lib/libm.tbd, missing required architecture armv7 in file /Applications/Xcode10.2.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS12.2.sdk/usr/lib/libm.tbdld: warning: ignoring file /Applications/Xcode10.2.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS12.2.sdk/usr/lib/libSystem.tbd, missing required architecture armv7 in file /Applications/Xcode10.2.app/Contents/Developer/Platforms/AppleTVOS.platform/Developer/SDKs/AppleTVOS12.2.sdk/usr/lib/libSystem.tbd
15:11:47 
15:11:47 Undefined symbols for architecture armv7:
15:11:47   "___error", referenced from:
```

Tested with Kodi libretro implementation on AppleTVOS 13.1 using Xcode 11