AppleTVOS platform build fix
AppleTVOS platform build fix

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
libretro/libretro-2048,libretro/libretro-2048,libretro/libretro-2048,libretro/libretro-2048