pixman: Fix nativesdk rebuilds for armv7a

MACHINE=X bitbake nativesdk-pixman; MACHINE=Y bitbake nativesdk-pixman

where X is an armv7a machine and Y is not results in pixman rebuilding due to the neon option. This is incorrect. The ultimate fix will be not to apply target system overrides in the nativesdk case. Until we do that we can at least work around the issue as done by this patch.

---

index 742a066..36d9b2d 100644
@@ -20,6 +20,7 @@ PE = "1"
 IWMMXT = "--disable-arm-iwmmxt"
 LOONGSON_MMI = "--disable-loongson-mmi"
 NEON = " --disable-arm-neon "
+NEON_class-nativesdk = " --disable-arm-neon "
 NEON_armv7a = " "
 NEON_armv7a-vfp-neon = " "