core/simd/x86: Use the none calling convention for intrinsics

The LLVM intrinsics that live under `llvm.x86` are not actual functions,
so trying to invoke them as such using the platform's native C
calling convention causes incorrect types to be emitted in the IR.

Thanks to laytanl for assistance in testing.

core/simd/x86/pclmulqdq.odin

@@ -6,7 +6,7 @@ _mm_clmulepi64_si128 :: #force_inline proc "c" (a, b: __m128i, $IMM8: u8) -> __m
 	return pclmulqdq(a, b, u8(IMM8))
 }
 
-@(private, default_calling_convention="c")
+@(private, default_calling_convention="none")
 foreign _ {
 	@(link_name="llvm.x86.pclmulqdq")
 	pclmulqdq :: proc(a, round_key: __m128i, #const imm8: u8) -> __m128i ---