Added support of building clang-upc and clang-upc2c with configure.

	* autoconf/configure.ac
	  Add enable/disable build of UPC to C translator.
	    --enable-clang-upc2c=[yes,no]
              Configure will check if the source code for upc2c is present
	      and issue appropriate error. Default is to build it if
	      tools/clang/tools/upc2c directory is available.
	    --with-upc-pts=[packed,struct]
	    --with-upc-packed-bits=[thread,phase,vaddr]
	    --with-upc-vaddr-order=[first,last]
              Provide default values for compile options.
	* configure, Regenerate. NOTE: autoconf 2.60 and aclocal 1.9.6
	  are required.
	* Makefile.configure.in, Add support for enable/disable of
	  UPC to C translator.
	* include/llvm/Config/config.h.in, Regenerate.