Android: Set debugger sysroot also for recent Ndk versions

Android debug support specifies the sysroot inside the used Ndk.

Recent Ndk versions have a different folder structure which moved the
sysroot location inside the Ndk to somewhere else. This change adds
finding the sysroot in the new directory layout in case it cannot be
found in the traditional location.

Instead of Ndk version checks, this code uses FilePath::exists to see if
the sysroot is valid.

Fixes: QTCREATORBUG-26814
Change-Id: I37db3043e405b83168d7c80c522d31bc148e458c
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

src/plugins/android/androidconfigurations.cpp

@@ -881,7 +881,7 @@ bool AndroidConfig::isValidNdk(const QString &ndkLocation) const
     const FilePath ndkPlatformsDir = ndkPath.pathAppended("platforms");
     if (version.majorVersion() <= 22
             && (!ndkPlatformsDir.exists() || ndkPlatformsDir.toString().contains(' ')))
-        return false; // TODO: Adapt code that assumes the presence of a "platforms" folder
+        return false;
 
     return true;
 }