Expose wait4 as wait4 rather than __wait4.

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

Change-Id: I5296d0cfec5546709cda990abd705ad33d7c4626
diff --git a/libc/arch-mips/syscalls/wait4.S b/libc/arch-mips/syscalls/wait4.S
new file mode 100644
index 0000000..8e3d2dc
--- /dev/null
+++ b/libc/arch-mips/syscalls/wait4.S
@@ -0,0 +1,22 @@
+/* autogenerated by gensyscalls.py */
+#include <sys/linux-syscalls.h>
+    .text
+    .globl wait4
+    .align 4
+    .ent wait4
+
+wait4:
+    .set noreorder
+    .cpload $t9
+    li $v0, __NR_wait4
+    syscall
+    bnez $a3, 1f
+    move $a0, $v0
+    j $ra
+    nop
+1:
+    la $t9,__set_errno
+    j $t9
+    nop
+    .set reorder
+    .end wait4