Introduce HAVE_AOUT symbol to remove hard-coded arch list for BINFMT_AOUT

HAVE_AOUT doesn't quite do the same thing as the recently removed
ARCH_SUPPORTS_AOUT config option. That was set even on platforms where
binfmt_aout isn't supported, although it's not entirely clear why.

So it's best just to introduce a new symbol, handled consistently with
other similar HAVE_xxx symbols; with a simple 'select' in the arch Kconfig.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
diff --git a/arch/um/Kconfig.i386 b/arch/um/Kconfig.i386
index 2a44e5c..1f57c11 100644
--- a/arch/um/Kconfig.i386
+++ b/arch/um/Kconfig.i386
@@ -9,8 +9,9 @@
 	default y
 
 config X86_32
-       bool
-       default y
+	bool
+	default y
+  	select HAVE_AOUT
 
 config RWSEM_XCHGADD_ALGORITHM
 	def_bool y