Remove the useless _C_LABEL from generated system calls.

Change-Id: Id1d2fd39972652831ea825f6f9cf940b08f42b5c
diff --git a/libc/arch-arm64/syscalls/__ptrace.S b/libc/arch-arm64/syscalls/__ptrace.S
index aa41071..ee63cb0 100644
--- a/libc/arch-arm64/syscalls/__ptrace.S
+++ b/libc/arch-arm64/syscalls/__ptrace.S
@@ -19,4 +19,4 @@
 
     ret
 END(__ptrace)
-.hidden _C_LABEL(__ptrace)
+.hidden __ptrace