Add support for building Clang UPC with configure/Makefile structure.
Fixes #31.

runtime/Makefile
	Enable building of UPC library.
runtime/libupc/Makefile
	New. Main makefile for building libupc.
runtime/libupc/Makefile.optional.in
	New. Makefile build options that are included at the top of the
        Makefile.
runtime/libupc/Makefile.rules.in
	New. Makefile rules an options.
runtime/libupc/config.h.in
	New. Libupc configure defines.
runtime/libupc/configure
	New. Regenerate from autoconf/configure.ac.
tools/driver/Makefile
	Add aliases for clang-upc and upc.
runtime/libupc/autoconf/configure.ac
runtime/libupc/autoconf/AutoRegen.sh
runtime/libupc/autoconf/ExportMap.map
runtime/libupc/autoconf/LICENSE.TXT
runtime/libupc/autoconf/aclocal.m4
runtime/libupc/autoconf/config.guess
runtime/libupc/autoconf/config.sub
runtime/libupc/autoconf/install-sh
runtime/libupc/autoconf/ltmain.sh
runtime/libupc/autoconf/m4/build_exeext.m4
runtime/libupc/autoconf/m4/c_printf_a.m4
runtime/libupc/autoconf/m4/check_gnu_make.m4
runtime/libupc/autoconf/m4/config_makefile.m4
runtime/libupc/autoconf/m4/config_project.m4
runtime/libupc/autoconf/m4/cxx_flag_check.m4
runtime/libupc/autoconf/m4/find_std_program.m4
runtime/libupc/autoconf/m4/func_isinf.m4
runtime/libupc/autoconf/m4/func_isnan.m4
runtime/libupc/autoconf/m4/func_mmap_file.m4
runtime/libupc/autoconf/m4/header_mmap_anonymous.m4
runtime/libupc/autoconf/m4/huge_val.m4
runtime/libupc/autoconf/m4/libtool.m4
runtime/libupc/autoconf/m4/link_options.m4
runtime/libupc/autoconf/m4/linux_mixed_64_32.m4
runtime/libupc/autoconf/m4/ltdl.m4
runtime/libupc/autoconf/m4/need_dev_zero_for_mmap.m4
runtime/libupc/autoconf/m4/path_tclsh.m4
runtime/libupc/autoconf/m4/rand48.m4
runtime/libupc/autoconf/m4/sanity_check.m4
runtime/libupc/autoconf/m4/single_cxx_check.m4
runtime/libupc/autoconf/m4/visibility_inlines_hidden.m4
runtime/libupc/autoconf/mkinstalldirs
        All the files under libupc/autoconf are copied from
        llvm/projects/simple.  All of them are identical to their source
        except for configure.ac which was modified for libupc configuration.
Factor code for building upc-related link options
Add UPC link support for NetBSD

This is sufficient to compile and link a UPC "Hello, World!" program
with clang-upc on NetBSD-6.1.4/amd64.  However, the runtime fails at
startup:

$ ./a.out -n1
./a.out: UPC initialization failed.
./a.out: reason: Invalid argument
Abort trap (core dumped)

Additionally, I needed to pass -DLIBUPC_ENABLE_BACKTRACE=FALSE to
cmake due to a lack of backtrace() and backtrace_symbols() in
NetBSD-6.  They are introduced in NetBSD-7.0, but in a separate
libexecinfo.
Add UPC link support for FreeBSD

This is sufficient to compile and link a UPC "Hello, World!" program
with clang-upc on FreeBSD-10.0-RELEASE-p4/amd64.  However, the runtime
fails at startup:

$ ./a.out -n1
./a.out: UPC initialization failed.
./a.out: reason: Invalid argument
Abort trap (core dumped)

Additionally, I needed to pass -DLIBUPC_ENABLE_BACKTRACE=FALSE to
cmake.  While backtrace() and backtrace_symbols() are present in
FreeBSD-10.0 (though missing in earlier releases), are in a separate
libexecinfo.  Some additional logic could/should be added to link with
"-lexecinfo" when backtrace support is enabled on FreeBSD.