When used, these targets end up with calls to undefined functions for all
of the various special vector stuff ispc needs to compile ispc programs
(masked store, gather, min/max, sqrt, etc.).
These targets are not yet useful for anything, but are a step toward
having an option to C++ code with calls out to intrinsics.
Reorganized the directory structure a bit and put the LLVM bitcode used
to define target-specific stuff (as well as some generic built-ins stuff)
into a builtins/ directory.
Note that for building on Windows, it's now necessary to set a LLVM_VERSION
environment variable (with values like LLVM_2_9, LLVM_3_0, LLVM_3_1svn, etc.)
MSVC 2010 issues an error if given a string larger than 64k characters
long. To work around this, the pre-processed stdlib.ispc code is now
stored as an array of characters terminated with a NUL (i.e. the same thing
in the end); MSVC is fine with arrays larger than 64k characters.
