Remove the useless _C_LABEL from generated system calls.

Change-Id: Id1d2fd39972652831ea825f6f9cf940b08f42b5c
diff --git a/libc/arch-mips64/syscalls/__set_tid_address.S b/libc/arch-mips64/syscalls/__set_tid_address.S
index ce1fcf5..8757001 100644
--- a/libc/arch-mips64/syscalls/__set_tid_address.S
+++ b/libc/arch-mips64/syscalls/__set_tid_address.S
@@ -23,4 +23,4 @@
     move ra, t0
     .set pop
 END(__set_tid_address)
-.hidden _C_LABEL(__set_tid_address)
+.hidden __set_tid_address