* If compiling on X86 or Sparc, automagically enable the JIT for that arch

* Setting ENABLE_X86_JIT or ENABLE_SPARC_JIT on the `make' command-line will
  force the inclusion of that JIT on a different architecture
* If neither JIT is enabled (e.g., compiling on a different architecture), the
  -march option will not be available to LLI.
* As a side effect of the $ARCH variable, the Sparc LLI can now link just a bit
  faster by not including the x86 library.

llvm-svn: 7070