Expose wait4 as wait4 rather than __wait4.

This helps strace(1) compile with one fewer hack.

Change-Id: I5296d0cfec5546709cda990abd705ad33d7c4626
diff --git a/libc/bionic/wait.cpp b/libc/bionic/wait.cpp
new file mode 100644
index 0000000..7dbcec2
--- /dev/null
+++ b/libc/bionic/wait.cpp
@@ -0,0 +1,54 @@
+/*
+ * Copyright (C) 2008 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 <sys/wait.h>
+#include <stddef.h>
+
+extern "C" int __waitid(idtype_t which, id_t id, siginfo_t* info, int options, struct rusage* ru);
+
+pid_t wait(int* status) {
+  return wait4(-1, status, 0, NULL);
+}
+
+pid_t wait3(int* status, int options, struct rusage* rusage) {
+  return wait4(-1, status, options, rusage);
+}
+
+pid_t waitpid(pid_t pid, int* status, int options) {
+  return wait4(pid, status, options, NULL);
+}
+
+int waitid(idtype_t which, id_t id, siginfo_t* info, int options) {
+  /* the system call takes an option struct rusage that we don't need */
+  return __waitid(which, id, info, options, NULL);
+}
+
+// TODO: remove this backward compatibility hack (for jb-mr1 strace binaries).
+extern "C" pid_t __wait4(pid_t pid, int* status, int options, struct rusage* rusage) {
+  return wait4(pid, status, options, rusage);
+}