Remove the useless _C_LABEL from generated system calls.

Change-Id: Id1d2fd39972652831ea825f6f9cf940b08f42b5c
diff --git a/libc/arch-arm64/syscalls/__waitid.S b/libc/arch-arm64/syscalls/__waitid.S
index 4244018..66e986a 100644
--- a/libc/arch-arm64/syscalls/__waitid.S
+++ b/libc/arch-arm64/syscalls/__waitid.S
@@ -19,4 +19,4 @@
 
     ret
 END(__waitid)
-.hidden _C_LABEL(__waitid)
+.hidden __waitid