libc: Add missing waitid() implementation.

Change-Id: I312ee608dbf9249e4886a10d45d13e3cda8a9042
diff --git a/libc/arch-arm/syscalls.mk b/libc/arch-arm/syscalls.mk
index f1d8fb1..c364d1c 100644
--- a/libc/arch-arm/syscalls.mk
+++ b/libc/arch-arm/syscalls.mk
@@ -3,7 +3,7 @@
 syscall_src += arch-arm/syscalls/_exit.S
 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/__waitid.S
 syscall_src += arch-arm/syscalls/__sys_clone.S
 syscall_src += arch-arm/syscalls/execve.S
 syscall_src += arch-arm/syscalls/__setuid.S
diff --git a/libc/arch-arm/syscalls/waitid.S b/libc/arch-arm/syscalls/__waitid.S
similarity index 86%
rename from libc/arch-arm/syscalls/waitid.S
rename to libc/arch-arm/syscalls/__waitid.S
index 4134e53..fdd0da3 100644
--- a/libc/arch-arm/syscalls/waitid.S
+++ b/libc/arch-arm/syscalls/__waitid.S
@@ -2,12 +2,12 @@
 #include <sys/linux-syscalls.h>
 
     .text
-    .type waitid, #function
-    .globl waitid
+    .type __waitid, #function
+    .globl __waitid
     .align 4
     .fnstart
 
-waitid:
+__waitid:
     mov     ip, sp
     .save   {r4, r5, r6, r7}
     stmfd   sp!, {r4, r5, r6, r7}