um: disable CMPXCHG_DOUBLE as it breaks UML build

Commit b789ef51 ("slub: Add cmpxchg_double_slab()") tests for
cmpxchg_double support in the SLUB code and it breaks UML builds with
SLUB.  Since UML does not support checking for CPU features, disable
CMPXCHG_DOUBLE just like CMPXCHG_LOCAL is disabled for UML.
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Reviewed-by: NChristoph Lameter <cl@linux.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/um/Kconfig.x86

@@ -10,6 +10,10 @@ config CMPXCHG_LOCAL
 	bool
 	default n
 
+config CMPXCHG_DOUBLE
+	bool
+	default n
+
 source "arch/x86/Kconfig.cpu"
 
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