TODO

Better integration of C library functions (memcpy, etc).
  Newlib provides generic versions of memcpy/memset/etc, however implementations
  in Lisp will perform better. Figure out how to override newlib's functions.
  LLVM's memcpy/memset intrinsics already call into Lisp.
  Consider replacing newlib's generic math functions too.

Improved syscall interface.
  Unix syscalls (open/close/read/write/etc) currently are performed by calling
  undefined C functions that have Lisp implementations.
  Using undefined functions will probably mess up a future linker implementation
  and a better approach will be needed.

Vector/SIMD support.
  LLVM vector operations are currently converted to scalar code.

C++ support.
  Will initally require porting compiler-rt, libc++abi, and libc++.
  C++ exceptions will require PNaCl's SjLj exception lowering pass as well.

Represent i1 as generalized booleans.
  i1 integers are currently implemented using regular integers,
  using booleans should improve performance.

Support NAN/+INF/-INF float values.