Bug 7003: Expose compiler back-end name in Jam build scripts

* sources/lib/build-system/jam-build.dylan (make-jam-state): Set the
  $(COMPILER_BACK_END) variable within the Jam state when executing build
  scripts.

* sources/lib/build-system/build.dylan (build-system): Pass the
  compiler-back-end to make-jam-state when available.

* sources/project-manager/projects/compilation.dylan (link-library): Pass the
  project's compiler-back-end to build-system when available.

* sources/project-manager/projects/implementation.dylan
  (remove-build-products): Pass the project's compiler-back-end to build-system
  when available.
Bug 7003: Move and refactor HARP build-scripts on POSIX platforms

* sources/jamfiles/mini-jambase.jam: Copy here from sources/lib/run-time.

* sources/jamfiles/posix-build.jam: New Jam include file containing
  rules common to HARP back-end linking on FreeBSD and Linux.

* sources/jamfiles/x86-linux-build.jam: Jam build script for Linux,
  refactored to 'include' posix-build.jam.

* sources/lib/run-time/pentium-linux/x86-linux-build.jam: Remove.

* sources/lib/run-time/pentium-linux/Makefile.in: Change to account for
  moved build scripts.

* sources/jamfiles/x86-freebsd-build.jam: Jam build script for FreeBSD,
  refactored to 'include' posix-build.jam.

* sources/lib/run-time/pentium-freebsd/x86-freebsd-build.jam: Remove.

* sources/lib/run-time/pentium-freebsd/Makefile.in: Change to account for
  moved build scripts.
Bug 7003: Relocate win32 jamfiles

* sources/lib/run-time/pentium-win32/x86-win32-pellesc-build.jam,
  sources/lib/run-time/pentium-win32/x86-win32-vc6-build.jam,
  sources/lib/run-time/pentium-win32/x86-win32-vc7-build.jam,
  sources/lib/run-time/pentium-win32/x86-win32-vc8-build.jam: Moved from here.

* sources/jamfiles/x86-win32-pellesc-build.jam,
  sources/jamfiles/x86-win32-vc6-build.jam,
  sources/jamfiles/x86-win32-vc7-build.jam,
  sources/jamfiles/x86-win32-vc8-build.jam: Moved to here.

* sources/lib/run-time/pentium-win32/makefile: Install from new
  location of win32 .jam files.
Bug 7458: Let dfmc-llvm-linker emit (currently empty) _glue.bc files

* sources/dfmc/llvm-linker/llvm-gluefile.dylan (emit-gluefile): Emit an
  empty _glue.bc bitcode file within the build directory of built libraries.
Bug 7003 7458: Add llvm-back-end support to the POSIX build scripts

* sources/jamfiles/posix-build.jam: When using the llvm back-end, use
  clang as the $(CC) command, and pass bitcode files directly to the
  clang link step.

* sources/jamfiles/x86-freebsd-build.jam,
  sources/jamfiles/x86-linux-build.jam: Separate out runtime object file
  names by the corresponding back-end used.
Bug 7003: Adapt posix-build.jam for the C back-end on Linux and FreeBSD

* configure.ac: Use AC_PROG_CC to obtain @CC@ and @CFLAGS@. Move config.jam
  to sources/jamfiles.

* sources/dfmc/c-run-time/config.jam.in: Remove from here.

* sources/jamfiles/config.jam.in: Move to here.

* sources/jamfiles/Makefile.in: Install generated *.jam files.

* sources/lib/run-time/mini-jambase.jam: Remove from here.

* sources/jamfiles/posix-build.jam: Refactor to support C back-end.

* sources/dfmc/c-run-time/c-freebsd-build.jam,
  sources/dfmc/c-run-time/c-linux-build.jam,
  sources/dfmc/c-run-time/x86-linux-build.jam,
  sources/dfmc/c-run-time/x86_64-linux-build.jam: Removed from here.

* sources/jamfiles/x86-freebsd-build.jam,
  sources/jamfiles/x86-linux-build.jam: Move common code out of
  platform-specific files, and move potentially platform-specific code
  into them.

* sources/jamfiles/x86_64-linux-build.jam: Moved here and harmonized
  with other posix target-specific build scripts.

* sources/dfmc/c-run-time/Makefile.in: Remove references to deleted
  build scripts.
Bug 7003: Respect executable: settings in project files

* sources/jamfiles/posix-build.jam
  (rule DylanLibrary): Store a library's computed -l$(name) name computed
   using FLIBName.
  (rule DylanLibraryClosure): Use stored computed names for libraries.
  (rule FDLLName): Respect $(image[2]) (the Executable: name) if one
   is provided.
  (rule FLIBName): New rule for computing -l names for libraries, respecting
   $(image[2]) (the Executable: name) if one is provided.
Bug 7003: Adapt Darwin c-back-end build to use the unified build script

* sources/dfmc/c-run-time/x86-darwin-build.jam,
  sources/dfmc/c-run-time/x86_64-darwin-build.jam,
  sources/dfmc/c-run-time/ppc-darwin-build.jam: Remove from here.

* sources/dfmc/c-run-time/common.jam: Remove (now unused).

* sources/jamfiles/x86-darwin-build.jam,
  sources/jamfiles/x86_64-darwin-build.jam,
  sources/jamfiles/ppc-darwin-build.jam: Move here and harmonize with
  the other posix build scripts.

* sources/dfmc/c-run-time/Makefile.in: Remove references to build scripts.
Bug 7003: Whitespace cleanup of posix-build.jam common build script