This is currently only used to decide whether it's worth doing an
"are all lanes running" check at the start of functions--for small
functions, it's not worth the overhead.
The cost is estimated relatively early in compilation (e.g. before
we know if an array access is a scatter/gather or not, before
constant folding, etc.), so there are many known shortcomings.
If no CPU is specified, use the host CPU type, not just a default of "nehalem".
Provide better features strings to the LLVM target machinery.
-> Thus ensuring that LLVM doesn't generate SSE>2 instructions for the SSE2
target (Fixes issue #82).
-> Slight code improvements from using cmovs in generated code now
Use the llvm popcnt intrinsic for the SSE2 target now (it now generates code
that doesn't call the popcnt instruction now that we properly tell LLVM
which instructions are and aren't available for SSE2.)
Set the Module's target appropriately when it's first created.
Compile separate 32 and 64 bit versions of the builtins-c bitcocde
and load the appropriate one based on the target we're compiling
for.
