Detect Android in configure

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

configure.ac

@@ -403,6 +403,23 @@ case "${build_os}" in
     ;;
 esac
 
+dnl Android is linux, but a bit different
+AS_IF([test "$SYS" = linux],[
+    AC_MSG_CHECKING([for an Android system])
+    AC_PREPROC_IFELSE([AC_LANG_PROGRAM(
+        [[#ifndef __ANDROID__
+         # error Not Android
+         #endif
+        ]],[[;]])
+    ],[
+      HAVE_ANDROID="1"
+      AC_MSG_RESULT([yes])
+    ],[
+      AC_MSG_RESULT([no])
+    ])
+])
+AM_CONDITIONAL(HAVE_ANDROID, test "${HAVE_ANDROID}" = "1")
+
 dnl
 dnl  Libtool
 dnl  It's very bad, but our former custom system was worst