Android: Detect clang and gdb from older NDK

Get some minimal compatibility with the older NDK that is used for
Qt < 5.12 back.
This detects clang-3.6 and gdb from NDK 10e.
For building, the android-g++ mkspec continues to be used for Qt < 5.12
(it uses Qt's default mkspec, regardless of toolchain in the kit,
because the toolchain reports to support both).

Task-number: QTCREATORBUG-21595
Change-Id: I3487c38093f43ccae2418fb28807a50fbda101a8
Reviewed-by: Andy Shaw <andy.shaw@qt.io>
Reviewed-by: BogDan Vatra <bogdan@kdab.com>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/android/androidtoolchain.cpp

@@ -109,7 +109,7 @@ void AndroidToolChain::addToEnvironment(Environment &env) const
 FileName AndroidToolChain::suggestedDebugger() const
 {
     // TODO: Make use of LLDB if available.
-    return AndroidConfigurations::currentConfig().gdbPath();
+    return AndroidConfigurations::currentConfig().gdbPath(targetAbi());
 }
 
 FileName AndroidToolChain::suggestedGdbServer() const