Fix statx feature test for Android

statx syscall was introduced in Android-30.
Compiling for Android<30 should fail, yet it doesn't, which results in false positive for a feature that is actually not available.
Would guess that this happens because of the same name for both the function and the struct, which is not #ifdef'ed for legacy Android.

Current check "host_system != 'android'" doesn't guard the feature test against android,
because host_system is never just android, it's android-$abi, like android-x86_64.
10 jobs for Android-statx-feature-test in 9 minutes and 43 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Style Check
passed check-todos #1082791

00:01:21

passed style-check-diff #1082790

00:01:27

 
  Build
passed cross-android_api21_arm64 #1082794

00:01:27

passed cross-android_api28_arm64 #1082795

00:01:27

passed cross-mingw64 #1082796

00:02:04

passed debian-stable-x86_64 #1082793

00:02:09

passed fedora-x86_64 #1082792

00:08:08

passed msys2-mingw32 #1082797
win32-ps

00:07:32

passed vs2017-x64 #1082798
win32-ps

00:08:07

 
  Coverage
passed coverage #1082799

00:01:34

76.1%