Remove the useless _C_LABEL from generated system calls.

Change-Id: Id1d2fd39972652831ea825f6f9cf940b08f42b5c
diff --git a/libc/arch-arm64/syscalls/__timer_getoverrun.S b/libc/arch-arm64/syscalls/__timer_getoverrun.S
index a458941..b11e356 100644
--- a/libc/arch-arm64/syscalls/__timer_getoverrun.S
+++ b/libc/arch-arm64/syscalls/__timer_getoverrun.S
@@ -19,4 +19,4 @@
 
     ret
 END(__timer_getoverrun)
-.hidden _C_LABEL(__timer_getoverrun)
+.hidden __timer_getoverrun