Add <sys/io.h>.

This is unusual in being inline-only, but these are (a) trivial functions, (b) ancient functions, and (c) unusable by apps. Plus they're arriving just too late for API 35, which definitely influenced by "this is silly" decision! They're also x86/x86-64 only, though that's a neutral argument because it would mean almost no-one will be affected no matter what choice we make here.

There is an argument for going the usual "callers should just have their own header-only implementation that they `-include` on the compiler command line" route, but the x86/x86-64 I/O port stuff isn't going away just yet, and LTP was also already working around the absence of these.

Bug: http://b/346990074
Test: treehugger
Change-Id: I6920266123104f2770875331efeefa5788014993
diff --git a/tests/sys_io_test.cpp b/tests/sys_io_test.cpp
new file mode 100644
index 0000000..293ceb2
--- /dev/null
+++ b/tests/sys_io_test.cpp
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <gtest/gtest.h>
+
+#include <sys/io.h>
+
+#include "utils.h"
+
+TEST(sys_io, iopl) {
+#if defined(__i386__) || defined(__x86_64__)
+  errno = 0;
+  ASSERT_EQ(-1, iopl(4));
+  ASSERT_ERRNO(EINVAL);
+#else
+  GTEST_SKIP() << "iopl requires x86/x86-64";
+#endif
+}
+
+TEST(sys_io, ioperm) {
+#if defined(__i386__) || defined(__x86_64__)
+  errno = 0;
+  ASSERT_EQ(-1, ioperm(65535, 4, 0));
+  ASSERT_ERRNO(EINVAL);
+#else
+  GTEST_SKIP() << "ioperm requires x86/x86-64";
+#endif
+}