Remove the useless _C_LABEL from generated system calls.

Change-Id: Id1d2fd39972652831ea825f6f9cf940b08f42b5c
diff --git a/libc/arch-x86_64/syscalls/__timer_getoverrun.S b/libc/arch-x86_64/syscalls/__timer_getoverrun.S
index 772b05e..fe71efe 100644
--- a/libc/arch-x86_64/syscalls/__timer_getoverrun.S
+++ b/libc/arch-x86_64/syscalls/__timer_getoverrun.S
@@ -14,4 +14,4 @@
 1:
     ret
 END(__timer_getoverrun)
-.hidden _C_LABEL(__timer_getoverrun)
+.hidden __timer_getoverrun