Since LLVM_NATIVE_ARCH, LLVM_NATIVE_ASMPARSER, LLVM_NATIVE_ASMPRINTER,
LLVM_NATIVE_DISASSEMBLER, LLVM_NATIVE_TARGET, LLVM_NATIVE_TARGETINFO and
LLVM_NATIVE_TARGETMC are already defined in llvm-config.h, there seems
to be no reason to also define them in config.h. Also, I can only find
usage of these macros in files that include llvm-config.h.
So let's remove the duplicated macros from config.h.