Disable early autovectorization of runtime
Disable early autovectorization of runtime

We compile the runtime modules to .ll for a "generic" target at -O3.
Apparently in some circumstances this autovectorizes to 128-bits. Not
all vector types are supported by all targets (hexagon), so this is bad,
and can cause assertion failures inside LLVM during instruction
selection. This PR turns this off.

The .ll gets a second chance to autovectorize later in codegen once the
module is assembled and has a concrete target.


Former-commit-id: 457ee7eaa6246419a2a2d0e5cd55f0a0279dd081
Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide