Add support for building Clang UPC with configure/Makefile structure.

Makefile.config.in
        Add conditional for enable/disable of UPC runtime building.
Makefile.rules
        Add support for more then one tool alias. For Clang UPC we create
        clang-upc and upc aliases beside clang++.
autoconf/configure.ac
        Add UPC required configuration switches.  NOTE: Some of the
        switches are duplicated in the libupc configure (e.g. pts
        representation, runtime model).
configure
        Regenerate.
include/llvm/Config/config.h.in
	Added Clang UPC configuration defines.