Added simd_extract_lsbs intrinsic as well.

Equivalent to the simd_extract_msbs intrinsic, except it extracts the
least significant bit of each element instead.

src/check_builtin.cpp

@@ -888,6 +888,7 @@ gb_internal bool check_builtin_simd_operation(CheckerContext *c, Operand *operan
 			return true;
 		}
 
+	case BuiltinProc_simd_extract_lsbs:
 	case BuiltinProc_simd_extract_msbs:
 		{
 			Operand x = {};