x86: Implement atomic[64]_dec_if_positive()

Add support for atomic_dec_if_positive(), and
atomic64_dec_if_positive() for x86-64.

atomic64_dec_if_positive() for x86-32 was already implemented in a previous patch.

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
LKML-Reference: <1267183361-20775-2-git-send-email-luca@luca-barbieri.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/lib/atomic64_test.c b/lib/atomic64_test.c
index 0effcac..58efdab 100644
--- a/lib/atomic64_test.c
+++ b/lib/atomic64_test.c
@@ -112,7 +112,7 @@
 	r += one;
 	BUG_ON(v.counter != r);
 
-#if defined(CONFIG_X86_32) || defined(CONFIG_MIPS) || defined(CONFIG_PPC) || defined(_ASM_GENERIC_ATOMIC64_H)
+#if defined(CONFIG_X86) || defined(CONFIG_MIPS) || defined(CONFIG_PPC) || defined(_ASM_GENERIC_ATOMIC64_H)
 	INIT(onestwos);
 	BUG_ON(atomic64_dec_if_positive(&v) != (onestwos - 1));
 	r -= one;