Add some configure/CMake options for enabling/disabling Subzero targets.

Makefile

 #===- ./Makefile -------------------------------------------*- Makefile -*--===#
 #
 #                     The LLVM Compiler Infrastructure
 #
 # This file is distributed under the University of Illinois Open Source
 # License. See LICENSE.TXT for details.
 #
 #===------------------------------------------------------------------------===#
 
 LEVEL := .
@@ skipping 196 matching lines @@
 # autoconf/configure.ac.
 # Note that Makefile.config is covered by its own separate rule
 # in Makefile.rules where it can be reused by sub-projects.
 #------------------------------------------------------------------------
 FilesToConfig := \
   bindings/ocaml/llvm/META.llvm \
   docs/doxygen.cfg \
   llvm.spec \
   include/llvm/Config/config.h \
   include/llvm/Config/llvm-config.h \
+  include/llvm/Config/SZTargets.def \
   include/llvm/Config/Targets.def \
   include/llvm/Config/AsmPrinters.def \
   include/llvm/Config/AsmParsers.def \
   include/llvm/Config/Disassemblers.def \
   include/llvm/Support/DataTypes.h
 FilesToConfigPATH  := $(addprefix $(LLVM_OBJ_ROOT)/,$(FilesToConfig))
 
 all-local:: $(FilesToConfigPATH)
 $(FilesToConfigPATH) : $(LLVM_OBJ_ROOT)/% : $(LLVM_SRC_ROOT)/%.in
         $(Echo) Regenerating $*
@@ skipping 72 matching lines @@
 # declare all targets at this level to be serial:
 
 .NOTPARALLEL:
 
 else # Building "Apple-style."
 # In an Apple-style build, once configuration is done, lines marked
 # "Apple-style" are removed with sed!  Please don't remove these!
 # Look for the string "Apple-style" in utils/buildit/build_llvm.
 include $(shell find . -name GNUmakefile) # Building "Apple-style."
 endif # Building "Apple-style."