Clean up and document our hacks for building BSD source.

Change-Id: Ic591e22fa5b363bb68376b9f25814c0e5bd83fbf

libc/upstream-openbsd/android/include/gd_qnan.h

@@ -0,0 +1,48 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+#if __arm__
+
+#define f_QNAN  0xffffffff
+
+#define d_QNAN0 0xffffffff
+#define d_QNAN1 0xffffffff
+
+#elif __mips__
+
+#define f_QNAN  0x7fbfffff
+
+#define d_QNAN0 0x7ff7ffff
+#define d_QNAN1 0xffffffff
+
+#else
+
+#define f_QNAN  0xffc00000
+
+#define d_QNAN0 0x00000000
+#define d_QNAN1 0xfff80000
+
+#endif
+
+/* long double. */
+#if __LP64__
+#define ld_QNAN0 0x7fff8000
+#define ld_QNAN1 0x00000000
+#define ld_QNAN2 0x00000000
+#define ld_QNAN3 0x00000000
+#else
+/* sizeof(long double) == sizeof(double), so we shouldn't be trying to use these constants. */
+#endif