Replacing C back-end with pure x86_64 assembly language
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This is a more challenging project than the parser replacement
project; in recognition of that, if you completely succeed with this
project (all test programs compile and run correctly), I will give you
5 additional extra credit points on your final grade.

The requirement here is to replace the C back-end
of the compiler with a pure x86_64 assembly language back-end.

You don't have to change anything in the parser or the lexer, but you
will have to: 

  1) Rewrite the compiler/emit.c code so that it emits only x86_64 assembly language.
  2) Rewrite the runtime/* it is completely in x86_64 assembly language, which
     means writing a memory allocator in assembly language to handle the simple
     allocation needs of Pleasant.
  3) Change the test environment so that it compiles with your new code (in particular,
     you will no longer need a valgrind in the Makefile, and you will probably have to
     make other changes).