Expose wait4 as wait4 rather than __wait4.

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

Change-Id: I5296d0cfec5546709cda990abd705ad33d7c4626
diff --git a/libc/arch-x86/syscalls/wait4.S b/libc/arch-x86/syscalls/wait4.S
new file mode 100644
index 0000000..e3bad3e
--- /dev/null
+++ b/libc/arch-x86/syscalls/wait4.S
@@ -0,0 +1,30 @@
+/* autogenerated by gensyscalls.py */
+#include <linux/err.h>
+#include <machine/asm.h>
+#include <sys/linux-syscalls.h>
+
+ENTRY(wait4)
+    pushl   %ebx
+    pushl   %ecx
+    pushl   %edx
+    pushl   %esi
+    mov     20(%esp), %ebx
+    mov     24(%esp), %ecx
+    mov     28(%esp), %edx
+    mov     32(%esp), %esi
+    movl    $__NR_wait4, %eax
+    int     $0x80
+    cmpl    $-MAX_ERRNO, %eax
+    jb      1f
+    negl    %eax
+    pushl   %eax
+    call    __set_errno
+    addl    $4, %esp
+    orl     $-1, %eax
+1:
+    popl    %esi
+    popl    %edx
+    popl    %ecx
+    popl    %ebx
+    ret
+END(wait4)