Accept Android platform by both CMake and configure

Accept Android platform by both CMake and configure
(fix of commit 1680d91)

* CMakeLists.txt (_HOST): Adjust FIXME comment.
* CMakeLists.txt (HOST): Remove replacement of "android" to "linux".
* CMakeLists.txt [CMAKE_USE_PTHREADS_INIT && HOST=*-*-android*]:
Define GC_THREADS and _REENTRANT macros.
* CMakeLists.txt [CMAKE_USE_PTHREADS_INIT && HOST=*-*-android*
&& enable_parallel_mark]: Define PARALLEL_MARK macro.
* CMakeLists.txt [CMAKE_USE_PTHREADS_INIT && HOST=*-*-android*
&& enable_thread_local_alloc]: Define THREAD_LOCAL_ALLOC macro.
* configure.ac [$THREADS=posix && $host=*-*-android*] (GC_THREADS,
_REENTRANT): Define macro.
* configure.ac [$THREADS=posix && $host=*-*-android*
&& $enable_parallel_mark] (PARALLEL_MARK): Likewise.
* configure.ac [$THREADS=posix && $host=*-*-android*
&& $enable_thread_local_alloc] (THREAD_LOCAL_ALLOC): Likewise.