configure.ac: fix detection of linux systems

configure.ac

@@ -134,15 +134,12 @@ case "$target" in
   libext=a
   AC_DEFINE(STARPU_HAVE_WINDOWS, [], [Define this on windows.])
   ;;
-esac
-AM_CONDITIONAL([STARPU_HAVE_WINDOWS], [test "x$starpu_windows" = "xyes"])
-
-case "$target_os" in
 *linux*)
   starpu_linux=yes
   ;;
 esac
-AM_CONDITIONAL(STARPU_LINUX_SYS, [test "x$starpu_linux" = "xyes"])
+AM_CONDITIONAL([STARPU_HAVE_WINDOWS], [test "x$starpu_windows" = "xyes"])
+AM_CONDITIONAL([STARPU_LINUX_SYS], [test "x$starpu_linux" = "xyes"])
 
 # on Darwin, GCC targets i386 by default, so we don't have atomic ops
 AC_CHECK_SIZEOF([void *])