Add android_dlopen_ext() interface to linker.

Add a function "android_dlopen_ext()", defined in <android/dlext.h>.
This is an extended version of dlopen() which takes a struct for passing
additional parameters for Android-specific functionality. This will be
used to support RELRO section sharing between separate processes.

Bug: 13005501
Change-Id: I9c99b2f2a02ee329dedaeba09ef3a1113b17b2d6

libc/include/android/dlext.h

@@ -0,0 +1,39 @@
+/*
+ * 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.
+ */
+
+#ifndef __ANDROID_DLEXT_H__
+#define __ANDROID_DLEXT_H__
+
+#include <stddef.h>
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+/* bitfield definitions for android_dlextinfo.flags */
+enum {
+  /* Mask of valid bits */
+  ANDROID_DLEXT_VALID_FLAG_BITS = 0,
+};
+
+typedef struct {
+  int     flags;
+} android_dlextinfo;
+
+extern void* android_dlopen_ext(const char* filename, int flag, const android_dlextinfo* extinfo);
+
+__END_DECLS
+
+#endif /* __ANDROID_DLEXT_H__ */