Allow clang to build host binaries.

Change-Id: I7e4f9dc6f69a97cfefdfa2ed55c5d7b8ad496da7

Conflicts:
	core/definitions.mk
	core/llvm_config.mk
Refactor llvm_config.mk and support the 2nd arch

1. Following the setup of gcc in build/core/combo/,
we added the [HOST|TARGET]_<arch>.mk clang config files,
and load only the configs needed by the current product.
2. Added support for the 2nd arch.

Change-Id: I2a383418a9688a050b39492f8e489d40eeeb5f2d

Conflicts:
	core/binary.mk
	core/executable_internal.mk
	core/llvm_config.mk
	core/shared_library_internal.mk
Switch to LLVM 3.4 prebuilts in AOSP.

Change-Id: I064e953fb1bf69e7e321616647aab88dcc39af76