Start SSE2 implementation based on SSE4.1 version

Wire up basic functions and features for SSE2 support using the SSE4.1 version
as a basis without implementing the SSE2 instructions yet.

 * Cargo.toml: add no_sse2 feature
 * benches/bench.rs: wire SSE2 benchmarks
 * build.rs: add SSE2 rust intrinsics and assembly builds
 * c/Makefile.testing: add SSE2 C and assembly targets
 * c/README.md: add SSE2 to C build instructions
 * c/blake3_c_rust_bindings/build.rs: add SSE2 C rust binding builds
 * c/blake3_c_rust_bindings/src/lib.rs: add SSE2 C rust bindings
 * c/blake3_dispatch.c: add SSE2 C dispatch
 * c/blake3_impl.h: add SSE2 C function prototypes
 * c/blake3_sse2.c: add SSE2 C intrinsic file starting with SSE4.1 version
 * c/blake3_sse2_x86-64_{unix.S,windows_gnu.S,windows_msvc.asm}: add SSE2
   assembly files starting with SSE4.1 version
 * src/ffi_sse2.rs: add rust implementation using SSE2 C rust bindings
 * src/lib.rs: add SSE2 rust intrinsics and SSE2 C rust binding rust SSE2 module
   configurations
 * src/platform.rs: add SSE2 rust platform detection and dispatch
 * src/rust_sse2.rs: add SSE2 rust intrinsic file starting with SSE4.1 version
 * tools/instruction_set_support/src/main.rs: add SSE2 feature detection

1 files changed, 1 insertions, 0 deletions

diff --git a/tools/instruction_set_support/src/main.rs b/tools/instruction_set_support/src/main.rs
index 15f9f37..6b509b0 100644
--- a/tools/instruction_set_support/src/main.rs
+++ b/tools/instruction_set_support/src/main.rs
@@ -1,6 +1,7 @@
 fn main() {
     #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
     {
+        dbg!(is_x86_feature_detected!("sse2"));
         dbg!(is_x86_feature_detected!("sse4.1"));
         dbg!(is_x86_feature_detected!("avx2"));
         dbg!(is_x86_feature_detected!("avx512f"));