Add tests for all C11 headers.

Well, all except <threads.h> which we have no current plans to implement.

The only thing this turned up is that clang's <float.h> doesn't define
FLT_HAS_SUBNORM/DBL_HAS_SUBNORM/LDBL_HAS_SUBNORM, so for now we assert
that those are missing so that when we get a fixed clang, we notice.

Also the <tgmath.h> is utterly perfunctory, but seems like an appropriate
amount of effort to put in.

Bug: N/A
Test: ran tests
Change-Id: I7f7a7040b3271ceda625bee8a40a9d8cef52ee44
diff --git a/tests/iso646_test.c b/tests/iso646_test.c
new file mode 100644
index 0000000..618f027
--- /dev/null
+++ b/tests/iso646_test.c
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <iso646.h>
+
+#if !defined(and)
+#error and
+#endif
+#if !defined(and_eq)
+#error and_eq
+#endif
+#if !defined(bitand)
+#error bitand
+#endif
+#if !defined(bitor)
+#error bitor
+#endif
+#if !defined(compl)
+#error compl
+#endif
+#if !defined(not)
+#error not
+#endif
+#if !defined(not_eq)
+#error not_eq
+#endif
+#if !defined(or)
+#error or
+#endif
+#if !defined(or_eq)
+#error or_eq
+#endif
+#if !defined(xor)
+#error xor
+#endif
+#if !defined(xor_eq)
+#error xor_eq
+#endif