Expose wait4 as wait4 rather than __wait4.

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

Change-Id: I5296d0cfec5546709cda990abd705ad33d7c4626
diff --git a/libc/arch-arm/syscalls.mk b/libc/arch-arm/syscalls.mk
index 5cb46b5..9eb5136 100644
--- a/libc/arch-arm/syscalls.mk
+++ b/libc/arch-arm/syscalls.mk
@@ -4,6 +4,7 @@
 syscall_src += arch-arm/syscalls/_exit_thread.S
 syscall_src += arch-arm/syscalls/__fork.S
 syscall_src += arch-arm/syscalls/__waitid.S
+syscall_src += arch-arm/syscalls/wait4.S
 syscall_src += arch-arm/syscalls/__sys_clone.S
 syscall_src += arch-arm/syscalls/execve.S
 syscall_src += arch-arm/syscalls/__setuid.S
@@ -180,7 +181,6 @@
 syscall_src += arch-arm/syscalls/ioprio_set.S
 syscall_src += arch-arm/syscalls/ioprio_get.S
 syscall_src += arch-arm/syscalls/uname.S
-syscall_src += arch-arm/syscalls/__wait4.S
 syscall_src += arch-arm/syscalls/umask.S
 syscall_src += arch-arm/syscalls/__reboot.S
 syscall_src += arch-arm/syscalls/__syslog.S
diff --git a/libc/arch-arm/syscalls/__wait4.S b/libc/arch-arm/syscalls/wait4.S
similarity index 91%
rename from libc/arch-arm/syscalls/__wait4.S
rename to libc/arch-arm/syscalls/wait4.S
index ac59045..7011099 100644
--- a/libc/arch-arm/syscalls/__wait4.S
+++ b/libc/arch-arm/syscalls/wait4.S
@@ -3,7 +3,7 @@
 #include <machine/asm.h>
 #include <sys/linux-syscalls.h>
 
-ENTRY(__wait4)
+ENTRY(wait4)
     mov     ip, r7
     ldr     r7, =__NR_wait4
     swi     #0
@@ -12,4 +12,4 @@
     bxls    lr
     neg     r0, r0
     b       __set_errno
-END(__wait4)
+END(wait4)