build/core: Remove extraneous `else' to fix build

Change-Id: Ic5253f55c8b22d7a1105b0b3c7918cb8c0fc4804
Rename TARGET_ARCH_VARIANT_CPU to TARGET_CPU_VARIANT

Changed in Android 4.3

Change-Id: I8efaf241fccb1c247bf32b361fba467ab33021b3